MINING  LIBRARY 


VOLUME  II 
PRINCIPLES  OF  MINING 

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PRINCIPLES    OF    MINING 

VALUATION,  ORGANIZATION 
AND   ADMINISTRATION 

COPPER,    GOLD,    LEAD,   SILVER,   TIN   AND   ZINC 


BY 

HERBERT  C.  HOOVER 

M 'ember  American  Institute  of  Mining  Engineers,  Mining  and  Metallurgical 

Society  of  America,  Societe  des  Ingenieurs  Civils  de  France, 

Fellow  Royal  Geographical  Society,  etc. 


FIRST  EDITION 
EIGHTH  IMPRESSION 


McGRAW-HILL  BOOK  COMPANY,  INC. 

239  WEST  39TH  STREET.    NEW  YORK 


LONDON:  HILL  PUBLISHING  CO.,  LTD. 
6  &  8  BOUVERIE  ST.,  E.  C. 


LJ  Hi'-;  A  iv  v 


Copyright,  1909,  BY  THE  HILL  PUBLISHING  COMPANY 

ENTERED  AT  STATIONERS'   HALL,  LONDON,  ENGLAND 


PREFACE. 

THIS  volume  is  a  condensation  of  a  series  of  lectures  delivered 
in  part  at  Stanford  and  in  part  at  Columbia  Universities.  It  is 
intended  neither  for  those  wholly  ignorant  of  mining,  nor  for 
those  long  experienced  in  the  profession. 

The  bulk  of  the  material  presented  is  the  common  heritage 
of  the  profession,  and  if  any  one  may  think  there  is  insufficient 
reference  to  previous  writers,  let  him  endeavor  to  find  to  whom 
the  origin  of  our  methods  should  be  credited.  The  science  has 
.grown  by  small  contributions  of  experience  since,  or  before,  those 
unnamed  Egyptian  engineers,  whose  works  prove  their  knowl- 
edge of  many  fundamentals  of  mine  engineering  six  thousand 
eight  hundred  years  ago.  If  I  have  contributed  one  sentence 
to  the  accumulated  knowledge  of  a  thousand  generations  of 
engineers,  or  have  thrown  one  new  ray  of  light  on  the  work,  I 
shall  have  done  my  share. 

I  therefore  must  acknowledge  my  obligations  to  all  those 
who  have  gone  before,  to  all  that  has  been  written  that  I  have 
read,  to  those  engineers  with  whom  I  have  been  associated  for 
many  years,  and  in  particular  to  many  friends  for  kindly  reply  to 
inquiry  upon  points  herein  discussed. 


iii 


CONTENTS. 


CHAPTER  I. 

PAGE 

VALUATION    OF    COPPER,    GOLD,    LEAD,   SILVER,    TIN,    AND    ZINC 

LODE  MINES     ...........        1 

Determination  of  average  metal  content;  sampling,  assay  plans, 
calculations  of  averages,  percentage  of  errors  in  estimate  from 
sampling. 

CHAPTER  II. 

MINE  VALUATION  (Continued) 13 

Calculation  of  quantities  of  ore,  and  classification  of  ore  in 
sight. 

CHAPTER  III. 

MINE  VALUATION  (Continued) 21 

Prospective  value.  Extension  in  depth ;  origin  and  structural 
character  of  the  deposit;  secondary  enrichment;  development  in 
neighboring  mines ;  depth  of  exhaustion. 


CHAPTER  IV. 

MINE  VALUATION  (Continued) 34 

Recoverable  percentage  of  the  gross  assay  value ;  price  of  metals ; 
cost  of  production. 

CHAPTER  V. 

MINE  VALUATION  (Continued) 42 

Redemption  or  amortization  of  capital  and  interest. 


CHAPTER  VI. 

MINE  VALUATION  (Concluded) 51 

Valuation  of  mines  with  little  or  no  ore  in  sight;  valuations  on 
second-hand  data ;  general  conduct  of  examinations ;  reports. 

v 


vi  CONTENTS. 


CHAPTER  VH. 

PAGE 

DEVELOPMENT  OF  MINES 58 

Entry  to  the  mine ;  tunnels ;  vertical,  inclined,  and  combined 
shafts ;  location  and  number  of  shafts. 

CHAPTER  VIII. 

DEVELOPMENT  OF  MINES  (Continued} 74 

Shape  and  size  of  shafts;  speed  of  sinking;  tunnels. 

CHAPTER  IX. 

DEVELOPMENT  OF  MINES  (Concluded) 84 

Subsidiary  development :  stations ;  crosscuts ;  levels ;  interval 
between  levels ;  protection  of  levels ;  winzes  and  rises.  Develop- 
ment in  the  prospecting  stage ;  drilling. 

CHAPTER  X. 

STOPING 94 

Methods  of  ore-breaking;  underhand stopes  ;  overhand  stopes ; 
combined  stope.  Valuing  ore  in  course  of  breaking. 

CHAPTER  XL 

METHODS  OF  SUPPORTING  EXCAVATION 103 

Timbering;  filling  with  waste ;  filling  with  broken  ore ;  pillars 
of  ore ;  artificial  pillars ;  caving  system. 

CHAPTER  XII. 

MECHANICAL  EQUIPMENT 124 

Conditions  bearing  on  mine  equipment;  winding  appliances; 
haulage  equipment  in  shafts;  lateral  underground  transport; 
transport  in  stopes. 

CHAPTER  XIII. 

MECHANICAL  EQUIPMENT  (Continued)  .        .        .     • 138 

Drainage:  controlling  factors;  volume  and  head  of  water; 
flexibility;  reliability;  power  conditions;  mechanical  efficiency; 
capital  outlay.  Systems  of  drainage,  —  steam  pumps,  compressed- 
air  pumps,  electrical  pumps,  rod -driven  pumps,  bailing;  com- 
parative value  of  various  systems. 


CONTENTS.  vii 

CHAPTER  XIV. 

PAGE 

MECHANICAL  EQUIPMENT  (Concluded)          .        .        .        .        .        .     145 

Machine  drilling :  power  transmission ;  compressed  air  vs.  elec- 
tricity ;  air  drills ;  machine  vs.  hand  drilling.  Workshops.  Im-' 
provement  in  equipment. 

CHAPTER  XV. 

RATIO  OF  OUTPUT  TO  THE  MINE 153 

Determination  of  possible  maximum ;  limiting  factors ;  cost  of 
equipment ;  life  of  the  mine ;  mechanical  inefficiency  of  patchwork 
plant ;  overproduction  of  base  metal ;  security  of  investment. 

CHAPTER  XVI. 

ADMINISTRATION 161 

Labor  efficiency ;  skill ;  intelligence ;  application  coordination ; 
contract  work ;  labor  unions ;  real  basis  of  wages. 

CHAPTER  XVII. 

ADMINISTRATION  (Continued)         .         .        .        .^__   .        .        .        .169 

Accounts  and  technical  data  and  reports ;  working  costs ;  divi- 
sion of  expenditure ;  inherent  limitations  in  accuracy  of  working 
costs ;  working  cost  sheets.  General  technical  data ;  labor,  sup- 
plies, power,  surveys,  sampling,  and  assaying. 

CHAPTER  XVIII. 

ADMINISTRATION  (Concluded) 178 

Administrative  reports. 

CHAPTER  XIX. 

THE  AMOUNT  OF  RISK  IN  MINING  INVESTMENTS       ....     181 

Risk  in  valuation  of  mines ;  in  mines  as  compared  with  other 
commercial  enterprises. 

CHAPTER  XX. 

THE    CHARACTER,   TRAINING,    AND   OBLIGATIONS  OF  THE   MINING 

ENGINEERING  PROFESSION 185 

INDEX  195 


PRINCIPLES   OF 


CHAPTER  I. 

VALUATION  OF  COPPER,  GOLD,  LEAD,  SILVER,  TIN,  AND  ZINC 

LODE  MINES. 

DETERMINATION  OF  AVERAGE  METAL  CONTENT;  SAMPLING,  ASSAY 
PLANS,  CALCULATIONS  OF  AVERAGES,  PERCENTAGE  OF  ERRORS 
IN  ESTIMATE  FROM  SAMPLING. 

THE  following  discussion  is  limited  to  in  situ  deposits  of 
copper,  gold,  lead,  silver,  tin,  and  zinc.  The  valuation  of  allu- 
vial deposits,  iron,  coal,  and  other  mines  is  each  a  special  science 
to  itself  and  cannot  be  adequately  discussed  in  common  with 
the  type  of  deposits  mentioned  above. 

The  value  of  a  metal  mine  of  the  order  under  discussion  de- 
pends upon :  - 

a.  The  profit  that  may  be  won  from  ore  exposed ; 

b.  The  prospective  profit  to  be  derived  from  extension  of  the 

ore  beyond  exposures; 

c.  The  effect  of  a  higher  or  lower  price  of  metal  (except  in 

gold  mines) ; 

d.  The  efficiency  of  the  management  during  realization. 

The  first  may  be  termed  the  positive  value,  and  can  be  ap- 
proximately determined  by  sampling  or  test-treatment  runs. 
The  second  and  the  third  may  be  termed  the  speculative  values, 
and  are  largely  a  matter  of  judgment  based  on  geological  evi- 
dence and  the  industrial  outlook.  The  fourth  is  a  question  of 
development,  equipment,  and  engineering  method  adapted  to  the 
prospects  of  the  enterprise,  together  with  capable  executive 
control  of  these  works. 

1 


2  PRINCIPLES  OF  MINING. 

It  should  be  stated  at  the  outset  that  it  is  utterly  impossible 
to  accurately  value  any  mine,  owing  to  the  many  speculative 
factors  involved.  The  best  that  can  be  done  is  to  state  that 
the  value  lies  between  certain  limits,  and  that  various  stages 
above  the  minimum  given  represent  various  degrees  of  risk. 
Further,  it  would  be  but  stating  truisms  to  those  engaged  in 
valuing  mines  to  repeat  that,  because  of  the  limited  life  of  every 
mine,  valuation  of  such  investments  cannot  be  based  upon  the 
principle  of  simple  interest ;  nor  that  any  investment  is  justified 
without  a  consideration  of  the  management  to  ensue.  Yet  the 
ignorance  of  these  essentials  is  so  prevalent  among  the  public 
that  they  warrant  repetition  on  every  available  occasion. 

To  such  an  extent  is  the  realization  of  profits  indicated  from 
the  other  factors  dependent  upon  the  subsequent  management 
of  the  enterprise  that  the  author  considers  a  review  of  under- 
ground engineering  and  administration  from  an  economic  point 
of  view  an  essential  to  any  essay  upon  the  subject.  While  the 
metallurgical  treatment  of  ores  is  an  essential  factor  in  mine 
economics,  it  is  considered  that  a  detailed  discussion  of  the 
myriad  of  processes  under  hypothetic  conditions  would  lead  too 
far  afield.  Therefore  the  discussion  is  largely  limited  to  under- 
ground and  administrative  matters. 

The  valuation  of  mines  arises  not  only  from  their  change  of 
ownership,  but  from  the  necessity  in  sound  administration  for  a 
knowledge  of  some  of  the  fundamentals  of  valuation,  such  as  ore 
reserves  and  average  values,  that  managerial  and  financial  policy 
may  be  guided  aright.  Also  with  the  growth  of  corporate  owner- 
ship there  is  a  demand  from  owners  and  stockholders  for  periodic 
information  as  to  the  intrinsic  condition  of  their  properties. 

The  growth  of  a  body  of  speculators  and  investors  in  mining 
stocks  and  securities  who  desire  professional  guidance  which 
cannot  be  based  upon  first-hand  data  is  creating  further  demand 
on  the  engineer.  Opinions  in  these  cases  must  be  formed  on 
casual  visits  or  second-hand  information,  and  a  knowledge  of 
men  and  things  generally.  Despite  the  feeling  of  some  engi- 
neers that  the  latter  employment  is  not  properly  based  profes- 
sionally, it  is  an  expanding  phase  of  engineers'  work,  and  must  be 


MINE   VALUATION.  3 

taken  seriously.  Although  it  lacks  satisfactory  foundation  for 
accurate  judgment,  yet  the  engineer  can,  and  should,  give  his 
experience  to  it  when  the  call  comes,  out  of  interest  to  the  in- 
dustry as  a  whole.  Not  only  can  he  in  a  measure  protect  the 
lamb,  by  insistence  on  no  investment  without  the  provision  of 
properly  organized  data  and  sound  administration  for  his  client, 
but  he  can  do  much  to  direct  the  industry  from  gambling  into 
industrial  lines. 

An  examination  of  the  factors  which  arise  on  the  valuation 
of  mines  involves  a  wide  range  of  subjects.  For  purposes  of 
this  discussion  they  may  be  divided  into  the  following  heads :  — 

1.  Determination  of  Average  Metal  Contents  of  the  Ore. 

2.  Determination  of  Quantities  of  Ore. 

3.  Prospective  Value. 

4.  Recoverable  Percentage  of  Gross  Value. 

5.  Price  of  Metals. 

6.  Cost  of  Production. 

7.  Redemption  or  Amortization  of  Capital  and  Interest. 

8.  Valuation  of  Mines  without  Ore  in  Sight. 

9.  General  Conduct  of  Examination  and  Reports. 

DETERMINATION  OF   AVERAGE   METAL  CONTENTS   OF   THE   ORE. 

Three  means  of  determination  of  the  average  metal  content 
of  standing  ore  are  in  use  —  Previous  Yield,  Test-treatment 
Runs,  and  Sampling. 

Previous  Yield.  —  There  are  certain  types  of  ore  where  the 
previous  yield  from  known  space  becomes  the  essential  basis  of 
determination  of  quantity  and  metal  contents  of  ore  standing 
and  of  the  future  probabilities.  Where  metals  occur  like  plums 
in  a  pudding,  sampling  becomes  difficult  and  unreliable,  and 
where  experience  has  proved  a  sort  of  regularity  of  recurrence 
of  these  plums,  dependence  must  necessarily  be  placed  on  past 
records,  for  if  their  reliability  is  to  be  questioned,  resort  must 
be  had  to  extensive  test-treatment  runs.  The  Lake  Superior 
copper  mines  and  the  Missouri  lead  and  zinc  mines  are  of  this 
type  of  deposit,  On  the  other  sorts  of  deposits  the  previous 


4  PRINCIPLES  OF  MINING. 

yield  is  often  put  forward  as  of  important  bearing  on  the  value 
of  the  ore  standing,  but  such  yield,  unless  it  can  be  authentically 
connected  with  blocks  of  ore  remaining,  is  not  necessarily  a 
criterion  of  their  contents.  Except  in  the  cases  mentioned,  and 
as  a  check  on  other  methods  of  determination,  it  has  little  place 
in  final  conclusions. 

Test  Parcels.  —  Treatment  on  a  considerable  scale  of  suffi- 
ciently regulated  parcels,  although  theoretically  the  ideal  method, 
is,  however,  not  often  within  the  realm  of  things  practical.  In 
examination  on  behalf  of  intending  purchasers,  the  time,  ex- 
pense, or  opportunity  to  fraud  are  usually  prohibitive,  even 
where  the  plant  and  facilities  for  such  work  exist.  Even  in 
cases  where  the  engineer  in  management  of  producing  mines  is 
desirous  of  determining  the  value  of  standing  ore,  with  the  ex- 
ception of  deposits  of  the  type  mentioned  above,  it  is  ordinarily 
done  by  actual  sampling,  because  separate  mining  'and  treat- 
ment of  test  lots  is  generally  inconvenient  and  expensive.  As  a 
result,  the  determination  of  the  value  of  standing  ore  is,  in  the 
great  majority  of  cases,  done  by  sampling  and  assaying. 

Sampling.  —  The  whole  theory  of  sampling  is  based  on  the 
distribution  of  metals  through  the  ore-body  with  more  or  less  reg- 
ularity, so  that  if  small  portions,  that  is  samples,  be  taken  from 
a  sufficient  number  of  points,  their  average  will  represent  fairly 
closely  the  unit  value  of  the  ore.  If  the  ore  is  of  the  extreme 
type  of  irregular  metal  distribution  mentioned  under  "  previous 
yield,"  then  sampling  has  no  place. 

How  frequently  samples  must  be  taken,  the  manner  of  taking 
them,  and  the  quantity  that  constitutes  a  fair  sample,  are 
matters  that  vary  with  each  mine.  So  much  depends  upon  the 
proper  performance  -of  this  task  that  it  is  in  fact  the  most 
critical  feature  of  mine  examination.  Ten  samples  properly 
taken  are  more  valuable  than  five  hundred  slovenly  ones,  like 
grab  samples,  for  such  a  number  of  bad  ones  would  of  a  surety 
lead  to  wholly^  wrong  conclusions.  Given  a  good  sampling  and 
a  proper  assay  plan,  the  valuation  of  a  mine  is  two-thirds  accom- 
plished. It  should  be  an  inflexible  principle  in  examinations  for 
purchase  that  every  sample  must  be  taken  under  the  personal 


MINE  VALUATION.  5 

supervision  of  the  examining  engineer  or  his  trusted  assistants. 
Aside  from  throwing  open  the  doors  to  fraud,  the  average  work- 
man will  not  carry  out  the  work  in  a  proper  manner,  unless 
under  constant  supervision,  because  of  his  lack  of  appreciation 
of  the  issues  involved.  Sampling  is  hard,  uncongenial,  manual 
labor.  It  requires  a  deal  of  conscientiousness  to  take  enough 
samples  and  to  take  them  thoroughly.  The  engineer  does  not 
exist  who,  upon  completion  of  this  task,  considers  that  he  has 
got  too  many,  and  most  wish  that  they  had  taken  more. 

The  accuracy  of  sampling  as  a  method  of  determining  the 
value  of  standing  ore  is  a  factor  of  the  number  of  samples  taken. 
The  average,  for  example,  of  separate  samples  from  each  square 
inch  would  be  more  accurate  than  those  from  each  alternate 
square  inch.  However,  the  accumulated  knowledge  and  ex- 
perience as  to  the  distribution  of  metals  through  ore  has  deter- 
mined approximately  the  manner  of  taking  such  samples,  and 
the  least  number  which  will  still  by  the  law  of  averages  secure 
a  degree  of  accuracy  commensurate  with  the  other  factors  of 
estimation. 

As  metals  are  distributed  through  ore-bodies  of  fissure  ori- 
gin with  most  regularity  on  lines  parallel  to  the  strike  and  dip, 
an  equal  portion  of  ore  from  every  point  along  cross-sections  at 
right  angles  to  the  strike  will  represent  fairly  well  the  average 
values  for  a  certain  distance  along  the  strike  either  side  of  these 
cross-sections.  In  massive  deposits,  sample  sections  are  taken 
in  all  directions.  The  intervals  at  which  sample  sections  must 
be  cut  is  obviously  dependent  upon  the  general  character  of  the 
deposit.  If  the  values  are  well  distributed,  a  longer  interval 
may  be  employed  than  in  one  subject  to  marked  fluctuations. 
As  a  general  rule,  five  feet  is  the  distance  most  accepted.  This, 
in  cases  of  regular  distribution  of  values,  may  be  stretched  to 
ten  feet,  or  in  reverse  may  be  diminished  to  two  or  three 
feet. 

The  width  of  ore  which  may -be  included  for  one  sample  is 
dependent  not  only  upon  the  width  of  the  deposit,  but  also  upon 
its  character.  Where  the  ore  is  wider  than  the  necessary  stop- 
ing  width,  the  sample  should  be  regulated  so  as  to  show  the 


8  PRINCIPLES   OF  MINING. 

possible  locus  of  values.  The  metal  contents  may  be,  and  often 
are,  particularly  in  deposits  of  the  impregnation  or  replacement 
type,  greater  along  some  streak  in  the  ore-body,  and  this  differ- 
ence may  be  such  as  to  make  it  desirable  to  stope  only  a  portion 
of  the  total  thickness.  For  deposits  narrower  than  the  neces- 
sary stoping  width  the  full  breadth  of  ore  should  be  included  in 
one  sample,  because  usually  the  whole  of  the  deposit  will  require 
to  be  broken. 

In  order  that  a  payable  section  may  not  possibly  be  diluted 
with  material  unnecessary  to  mine,  if  the  deposit  is  over  four 
feet  and  under  eight  feet,  the  distance  across  the  vein  or  lode  is 
usually  divided  into  two  samples.  If  still  wider,  each  is  confined 
to  a  .span  of  about  four  feet,  not  only  for  the  reason  given  above, 
but  because  the  more  numerous  the  samples,  the  greater  the 
accuracy.  Thus,  in  a  deposit  twenty  feet  wide  it  may  be  taken 
as  a  good  guide  that  a  test  section  across  the  ore-body  should  be 
divided  into  five  parts. 

As  to  the  physical  details  of  sample  taking,  every  engineer 
has  his  own  methods  and  safeguards  against  fraud  and  error.  In 
a  large  organization 'of  which  the  writer  had  for  some  years  the 
direction,  and  where  sampling  of  mines  was  constantly  in  prog- 
ress on  an  extensive  scale,  not  only  in  contemplation  of  purchase, 
but  where  it  was  also  systematically  conducted  in  operating 
mines  for  working  data,  he  adopted  the  above  general  lines  and 
required  the  following  details. 

A  fresh  face  of  ore  is  first  broken  and  then  a  trench  cut  about 
five  inches  wide  and  tWo  inches  deep.  This  trench  is  cut  with  a 
hammer  and  moil,  or,  where  compressed  air  is  available  and  the 
rock  hard,  a  small  air-drill  of  the  hammer  type  is  used.  The 
spoil  from  the  trench  forms  the  sample,  and  it  is  broken  down 
upon  a  large  canvas  cloth.  Afterwards  it  is  crushed  so  that  all 
pieces  will  pass  a  half-inch  screen,  mixed  and  quartered,  thus 
reducing  the  weight  to  half.  Whether  it  is  again  crushed  and 
quartered  depends  upon  what  the  conditions  are  as  'to  assaying. 
If  convenient  to  assay  office,  as  on  a  going  mine,  the  whole  of  the 
crushing  and  quartering  work  can  be  done  at  that  office,  where 
there  are  usually  suitable  mechanical  appliances.  If  the  samples 


MINE  VALUATION.  7 

must  be  taken  a  long  distance,  the  bulk  for  transport  can  be 
reduced  by  finer  breaking  and  repeated  quartering,  until  there 
remain  only  a  few  ounces. 

Precautions  against  Fraud.  —  Much  has  been  written  about 
the  precautions  to  be  taken  against  fraud  in  cases  of  valuations 
for  purchase.  The  best  safeguards  are  an  alert  eye  and  a  strong 
right  arm.  However,  certain  small  details  help.  A  large  leather 
bag,  arranged  to  lock  after  the  order  of  a  mail  sack,  into  which 
samples  can  be  put  underground  and  which  is  never  unfastened 
except  by  responsible  men,  not  only  aids  security  but  relieves 
the  mind.  A  few  samples  of  country  rock  form  a  good  check, 
and  notes  as  to  the  probable  value  of  the  ore,  from  inspection 
when  sampling,  are  useful.  A  great  help  in  examination  is  to 
have  the  assays  or  analyses  done  coincidentally  with  the  sam- 
pling. A  doubt  can  then  always  be  settled  by  resampling  at 
once,  and  much  knowledge  can  be  gained  which  may  relieve  so 
exhaustive  a  program  as  might  be  necessary  were  results  not 
known  until  after  leaving  the  mine. 

Assay  of  Samples.  —  Two  assays,  or  as  the  case  may  be, 
analyses,  are  usually  made  of  every  sample,  and  their  average 
taken.  In  the  case  of  erratic  differences  a  third  determination 
is  necessary. 

Assay  Plans.  —  An  assay  plan  is  a  plan  of  the  workings,  with 
the  location,  assay  value,  and  width  of  the  sample  entered  upon 
it.  In  a  mine  with  a  narrow  vein  or  ore-body,  a  longitudinal 
section  is  sufficient  base  for  such  entries,  but  with  a  greater  width 
than  one  sample  span  it  is  desirable  to  make  preliminary  plans 
of  separate  levels,  winzes,  etc.,  and  to  average  the  value  of  the 
whole  payable  widths  on  such  plans  before  entry  upon  a  longi- 
tudinal section.  Such  a  longitudinal  section  will,  through  the 
indicated  distribution  of  values,  show  the  shape  of  the  ore-body 
—  a  step  necessary  in  estimating  quantities  and  of  the  most 
fundamental  importance  in  estimating  the  probabilities  of  ore 
extension  beyond  the  range  of  the  openings.  The  final  assay 
plan  should  show  the  average  value  of  the  several  blocks  of 
ore,  and  it  is  from  these  averages  that  estimates  of  quantities 
must  be  made  up. 


8  PRINCIPLES   OF  MINING. 

Calculations  of  Averages.  —  The  first  step  in  arriving  at 
average  values  is  to  reduce  erratic  high  assays  to  the  general 
tenor  of  other  adjacent  samples.  This  point  has  been  dis- 
puted at  some  length,  more  often  by  promoters  than  by  engi- 
neers, but  the  custom  is  very  generally  and  rightly  adopted.  Er- 
ratically high  samples  may  indicate  presence  of  undue  metal  in 
the  assay  attributable  to  unconscious  salting,  for  if  the  value  be 
confined  to  a  few  large  particles  they  may  find  their  way 
through  all  the  quartering  into  the  assay.  Or  the  sample  may 
actually  indicate  rich  spots  of  ore ;  but  in  any  event  experience 
teaches  that  no  dependence  can  be  put  upon  regular  recurrence 
of  such  abnormally  rich  spots.  As  will  be  discussed  under  per- 
centage of  error  in  sampling,  samples  usually  indicate  higher 
than  the  true  value,  even  where  erratic  assays  have  been  elimi- 
nated. There  are  cases  of  profitable  mines  where  the  values 
were  all  in  spots,  and  an  assay  plan  would  show  80%  of  the 
assays  nil,  yet  these  pockets  were  so  rich  as  to  give  value  to  the 
whole.  Pocket  mines,  as  stated  before,  are  beyond  valuation  by 
sampling,  and  aside  from  the  previous  yield  recourse  must  be 
had  to  actual  treatment  runs  on  every  block  of  ore  separately. 

After  reduction  of  erratic  assays,  a  preliminary  study  of  the 
runs  of  value  or  shapes  of  the  ore-bodies  is  necessary  before  any 
calculation  of  averages.  A  preliminary  delineation  of  the  bounda- 
ries of  the  payable  areas  on  the  assay  plan  will  indicate  the  sec- 
tions of  the  mine  which  are  unpayable,  and  from  which  there- 
fore samples  can  be  rightly  excluded  in  arriving  at  an  average 
of  the  payable  ore  (Fig.  1).  In  a  general  way,  only  the  ore 
which  must  be  mined  need  be  included  in  averaging. 

The  calculation  of  the  average  assay  value  of  standing  ore 
from  samples  is  one  which  seems  to  require  some  statement  of 
elementals.  Although  it  may  seem  primitive,  it  can  do  no  harm 
to  recall  that  if  a  dump  of  two  tons  of  ore  assaying  twenty 
ounces  per  ton  be  added  to  a  dump  of  five  tons  averaging  one 
ounce  per  ton,  the  result  has  not  an  average  assay  of  twenty-one 
ounces  divided  by  the  number  of  dumps.  Likewise  one  sample 
over  a  width  of  two  feet,  assaying  twenty  ounces  per  ton,  if 
averaged  with  another  sample  over  a  width  of  five  feet,  assaying 


MINE  VALUATION.  9 

one  ounce,  is  no  more  twenty-one  ounces  divided  by  two  samples 
than  in  the  case  of  the  two  dumps.  If  common  sense  were  not 
sufficient  demonstration  of  this,  it  can  be  shown  algebraically. 
Were  samples  equidistant  from  each  other,  and  were  they  of  equal 
width,  the  average  value  would  be  the  simple  arithmetical  mean 
of  the  assays.  But  this  is  seldom  the  case.  The  number  of  in- 
stances, not  only  in  practice  but  also  in  technical  literature, 
where  the  fundamental  distinction  between  an  arithmetical  and 
a  geometrical  mean  is  lost  sight  of  is  amazing. 

To  arrive  at  the  average  value  of  samples,  it  is  necessary,  in 
effect,  to  reduce  them  to  the  actual  quantity  of  the  metal  and 
volume  of  ore  represented  by  each.  The  method  of  calculation 
therefore  is  one  which  gives  every  sample  an  importance  depend- 
ing upon  the  metal  content  of  the  volume  of  ore  it  represents. 

The  volume  of  ore  appertaining  to  any  given  sample  can  be 
considered  as  a  prismoid,  the  dimensions  of  which  may  be  stated 
as  follows  :  — 

W  =  Width  in  feet  of  ore  sampled. 
L  =  Length  in  feet  of  ore  represented  by  the  sample. 
D  =  Depth  into  the  block  to  which  values  are  assumed 
to  penetrate. 

We  may  also  let  :  — 

C  =  The  number  of  cubic  feet  per  ton  of  ore. 
V  =  Assay  value  of  the  sample. 

Then  =  tonnage  of  the  prismoid.* 

=  total  metal  contents. 


The  average  value,  of  a  number  of  samples  is  the  total  metal 
contents  of  their  respective  prismoids,  divided  by  the  total  ton- 
nage of  these  prismoids.  If  we  let  TF,  Wv  V,  F1;  etc.,  represent 
different  samples,  we  have:  — 

*  Strictly,  the  prismoidal  formula  should  be  used,  but  it  complicates  the 
study  unduly,  and  for  practical  purposes  the  above  may  be  taken  as  the 
volume. 


10  PRINCIPLES   OF  MINING. 


^,  =  average  value. 

C  C 

This  may  be  reduced  to:  — 

(VWLD)  +  (V.W^D,)  +  (7JTAD.,),  etc. 
(WLD)  +  (W^DJ  +  (W2L2DZ),  etc. 


As  a  matter  of  fact,  samples  actually  represent  the  value  of 
the  outer  shell  of  the  block  of  ore  only,  and  the  continuity  of 
the  same  values  through  the  block  is  a  geological  assumption. 
From  the  outer  shell,  all  the  values  can  be  taken  to  penetrate 
equal  distances  into  the  block,  and  therefore  D,  Dv  D2  may  be 
considered  as  equal  and  the  equation  becomes:  — 

(VWL)  +  (V,WM  +  (F2TF2L2),  etc. 
(WL)  +  (JFjLj)  +  (TF2L2),  etc. 

The  length  of  the  prismoid  base  L  for  any  given  sample  will 
be  a  distance  equal  to  one-half  the  sum  of  the  distances  to  the 
two  adjacent  samples.  As  a  matter  of  practice,  samples  are 
usually  taken  at  regular  intervals,  and  the  lengths  L,  Lv  L2  be- 
coming thus  equal  can  in  such  case  be  eliminated,  and  the  equa- 
tion becomes:  — 

(VW)  +  (VJVJ  +  (7Jfa),  etc. 
W  +Wl  +  W2,  etc. 

The  name  "assay  foot"  or  "foot  value"  has  been  given  to  the 
relation  VW,  that  is,  the  assay  value  multiplied  by  the  width 
sampled.*  It  is  by  this  method  that  all  samples  must  be  aver- 
aged. The  same  relation  obviously  can  be  evolved  by  using  an 
inch  instead  of  a  foot,  and  in  narrow  veins  the  assay  inch  is 
generally  used. 

Where  the  payable  cross-section  is  divided  into  more  than 
one  sample,  the  different  samples  in  the  section  must  be  averaged 
by  the  above  formula,  before  being  combined  with  the  adjacent 

*  An  error  will  be  found  in  this  method  unless  the  two  end  samples  be 
halved,  but  in  a  long  run  of  samples  this  may  be  disregarded. 


MINE  VALUATION.  11 

section.  Where  the  width  sampled  is  narrower  than  the  neces- 
sary stoping  width,  and  where  the  waste  cannot  be  broken  sepa- 
rately, the  sample  value  must  be  diluted  to  a  stoping  width.  To 
dilute  narrow  samples  to  a  stoping  width,  a  blank  value  over  the 
extra  width  which  it  is  necessary  to  include  must  be  averaged 
with  the  sample  from  the  ore  on  the  above  formula.  Cases  arise 
where,  although  a  certain  width  of  waste  must  be  broken  with 
the  ore,  it  subsequently  can  be  partially  sorted  out.  Practically 
nothing  but  experience  on  the  deposit  itself  will  determine  how 
far  this  will  restore  the  value  of  the  ore  to  the  average  of  the 
payable  seam.  In  any  event,  no  sorting  can  eliminate  all  such 
waste ;  and  it  is  necessary  to  calculate  the  value  on  the  breaking 
width,  and  then  deduct  from  the  gross  tonnage  to  be  broken  a 
percentage  from  sorting.  There  is  always  an  allowance  to  be 
made  in  sorting  for  a  loss  of  good  ore  with  the  discards. 

Percentage  of  Error  in  Estimates  from  Sampling.  —  It  must 
be  remembered  that  the  whole  theory  of  estimation  by  sampling 
is  founded  upon  certain  assumptions  as  to  evenness  of  continuity 
and  transition  in  value  and  volume.  It  is  but  a  basis  for  an  esti- 
mate, and  an  estimate  is  not  a  statement  of  fact.  It  cannot 
therefore  be  too  forcibly  repeated  that  an  estimate  is  inherently 
but  an  approximation,  take  what  care  one  may  in  its  founding. 
While  it  is  possible  to  refine  mathematical  calculation  of  averages 
to  almost  any  nicety,  beyond  certain  essentials  it  adds  nothing 
to  accuracy  and  is  often  misleading. 

It  is  desirable  to  consider  where  errors  are  most  likely  to 
creep  in,  assuming  that  all  fundamental  data  are  both  accurately 
taken  and  considered.  Sampling  of  ore  in  situ  in  general  has  a 
tendency  to  give  higher  average  value  than  the  actual  reduction 
of  the  ore  will  show.  On  three  West  Australian  gold  mines,  in 
records  covering  a  period  of  over  two  years,  where  sampling  was 
most  exhaustive  as  a  daily  regime  of  the  mines,  the  values  indi- 
cated by  sampling  were  12%  higher  than  the  mill  yield  plus  the 
contents  of  the  residues.  On  the  Witwatersrand  gold  mines, 
the  actual  extractable  value  is  generally  considered  to  be  about 
78  to  80%  of  the  average  shown  by  sampling,  while  the  mill 
extractions  are  on  average  about  90  to  92%  of  the  head  value 


12  PRINCIPLES  OF  MINING. 

coming  to  the  mill.  In  other  words,  there  is  a  constant  discrep- 
ancy of  about  10  to  12%  between  the  estimated  value  as  indi- 
cated by  mine  samples,  and  the  actual  value  as  shown  by  yield 
plus  the  residues.  '  At  Broken  Hill,  on  three  lead  mines,  the  yield 
is  about  12%  less  than  sampling  would  indicate.  This  constancy 
of  error  in  one  direction  has  not  been  so  generally  acknowledged 
as  would  be  desirable,  and  it  must  be  allowed  for  in  calculating 
final  results.  The  causes  of  the  exaggeration  seem  to  be :  — 

First,  inability  to  stope  a  mine  to  such  fine  limitations  of 
width,  or  exclusion  of  unpayable  patches,  as  would  appear  prac- 
ticable when  sampling,  that  is  by  the  inclusion  when  mining  of  a 
certain  amount  of  barren  rock.  Even  in  deposits  of  about  nor- 
mal stoping  width,  it  is  impossible  to  prevent  the  breaking  of  a 
certain  amount  of  waste,  even  if  the  ore  occurrence  is  regularly 
confined  by  walls. 

If  the  mine  be  of  the  impregnation  type,  such  as  those  at  Gold- 
field,  or  Kalgoorlie,  with  values  like  plums  in  a  pudding,  and  the 
stopes  themselves  directed  more  by  assays  than  by  any  physical 
differences  in  the  ore,  the  discrepancy  becomes  very  much  in- 
creased. In  mines  where  the  range  of  values  is  narrower  than  the 
normal  stoping  width,  some  wall  rock  must  be  broken.  Although 
it  is  customary  to  allow  for  this  in  calculating  the  average  value 
from  samples,  the  allowance  seldom  seems  enough.  In  mines 
where  the  ore  is  broken  on  to  the  top  of  stopes  filled  with  waste, 
there  is  some  loss  underground  through  mixture  with  the  filling. 

Second,  the  metal  content  of  ores,  especially  when  in  the  form 
of  sulphides,  is  usually  more  friable  than  the  matrix,  and  in  actual 
breaking  of  samples  an  undue  proportion  of  friable  material 
usually  creeps  in.  This  is  true  more  in  lead,  copper,  and  zinc, 
than  in  gold  ores.  On  several  gold  mines,  however,  tests  on 
accumulated  samples  for  their  sulphide  percentage  showed  a 
distinctly  greater  ratio  than  the  tenor  of  the  ore  itself  in  the  mill. 
As  the  gold  is  usually  associated  with  the  sulphides,  the  samples 
showed  higher  values  than  the  mill. 

In  general,  some  considerable  factor  of  safety  must  be 
allowed  after  arriving  at  calculated  average  of  samples,  —  how 
much  it  is  difficult  to  say,  but,  in  any  event,  not  less  than  10%. 


CHAPTER  II. 
MINE  VALUATION  (Continued). 

CALCULATION    OF    QUANTITIES    OF    ORE,    AND    CLASSIFICATION    OF 

ORE    IN   SIGHT. 

As  mines  are  opened  by  levels,  rises,  etc.,  through  the  ore,  an 
extension  of  these  workings  has  the  effect  of  dividing  it  into 
"  blocks."  The  obvious  procedure  in  determining  tonnages  is  to 
calculate  the  volume  and  value  of  each  block  separately.  Under 
the  law  of  averages,  the  multiplicity  of  these  blocks  tends  in 
proportion  to  their  number  to  compensate  the  percentage  of 
error  which  might  arise  in  the  sampling  or  estimating  of  any 
particular  one.  The  shapes  of  these  blocks,  on  longitudinal  sec- 
tion, are  often  not  regular  geometrical  figures.  As  a  matter  of 
practice,  however,  they  can  be  subdivided  into  such  figures 
that  the  total  will  approximate  the  whole  with  sufficient  close- 
ness for  calculations  of  their  areas. 

The  average  width  of  the  ore  in  any  particular  block  is  the 
arithmetical  mean  of  the  width  of  the  sample  sections  in  itx*  if 
the  samples  be  an  equal  distance  apart.  If  they  are  not  equi- 
distant, the  average  width  is  the  sum  of  the  areas  between 
samples,  divided  by  the  total  length  sampled.  The  cubic  foot 
contents  of  a  particular  block  is  obviously  the  width  multiplied 
by  the  area  of  its  longitudinal  section. 

The  ratio  of  cubic  feet  to  tons  depends  on  the  specific  gravity 
of  the  ore,  its  porosity,  and  moisture.  The  variability  of  ores 
throughout  the  mine  in  all  these  particulars  renders  any  method 
of  calculation  simply  an  approximation  in  the  end.  The  factors 
which  must  remain  unknown  necessarily  lead  the  engineer  to 

*  This  is  not  strictly  true  unless  the  sum  of  the  widths  of  the  two  end- 
sections  be  divided  by  two  and  the  result  incorporated  in  calculating  the 
means.  In  a  long  series  that  error  is  of  little  importance. 

13 


14  PRINCIPLES  OF  MINING. 

the  provision  of  a  margin  of  safety,  which  makes  mathematical 
refinement  and  algebraic  formulae  ridiculous. 

There  are  in  general  three  methods  of  determination  of  the 
specific  volume  of  ores :  — 

First,  by  finding  the  true  specific  gravity  of  a  sufficient  num- 
ber of  representative  specimens;  this,  however,  would  not  ac- 
count for  the  larger  voids  in  the  ore-body  and  in  any  event, 
to  be  anything  like  accurate,  would  be  as  expensive  as  sampling 
and  is  therefore  of  little  more  than  academic  interest. 

Second,  by  determining  the  weight  of  quantities  broken  from 
measured  spaces.  This  also  would  require  several  tests  from 
different  portions  of  the  mine,  and,  in  examinations,  is  usually 
inconvenient  and  difficult.  Yet  it  is  necessary  in  cases  of  un- 
usual materials,  such  as  leached  gossans,  and  it  is  desirable  to 
have  it  done  sooner  or  later  in  going  mines,  as  a  check. 

Third,  by  an  approximation  based  upon  a  calculation  from 
the  specific  gravities  of  the  predominant  minerals  in  the  ore. 
Ores  are  a  mixture  of  many  minerals;  the  proportions  vary 
through  the  same  ore-body.  Despite  this,  a  few  partial  analyses, 
which  are  usually  available  from  assays  of  samples  and  metal- 
lurgical tests,  and  a  general  inspection  as  to  the  compactness  of 
the  ore,  give  a  fairly  reliable  basis  for  approximation,  especially 
if  a  reasonable  discount  be  allowed  for  safety.  In  such  dis- 
count must  be  reflected  regard  for  the  porosity  of  the  ore,  and 
the  margin  of  safety  necessary  may  vary  from  10  to  25%.  If 
the  ore  is  of  unusual  character,  as  in  leached  deposits,  as  said 
before,  resort  must  be  had  to  the  second  method. 

The  following  table  of  the  weights  per  cubic  foot  and  the 
number  of  cubic  feet  per  ton  of  some  of  the  principal  ore- 
forming  minerals  and  gangue  rocks  will  be  useful  for  approxi- 
mating the  weight  of  a  cubic  foot  of  ore  by  the  third  method. 
Weights  are  in  pounds  avoirdupois,  and  two  thousand  pounds 
are  reckoned  to  the  ton. 


MINE  VALUATION. 


15 


WEIGHT  PER 
CUBIC  FOOT 


NUMBER  OK 
CUBIC  FEET 
PER  TON  OF 

'2000  LB. 


Antimony 417.50 

Sulphide 285.00 

Arsenical  Pyrites 371.87 

Barium  Sulphate 278.12 

Calcium,: 

Fluorite .  198.75 

Gypsum 145.62 

Calcite (  169.37 

Copper ' '  552.50 

Calcopyrite 262.50 

Bornite 321.87 

Malachite 247.50 

Azurite 237.50 

Chrysocolla 132.50 

Iron  (Cast) 450.00 

Magnetite 315.62 

Hematite 306.25 

Limonite 237.50 

Pyrite 312.50 

Carbonate 240.62 

Lead 710.62 

Galena 468.75 

Carbonate 406.87 

Manganese  Oxide 268.75 

Rhodonite 221.25 

Magnesite 187.50 

Dolomite 178.12 

Quartz 165.62 

Quicksilver 849.75 

Cinnabar 531.25 

Sulphur 127.12 

Tin        459.00 

Oxide 418.75 

Zinc '.     .     .  437.50 

Blende 253.12 

Carbonate 273.12 

Silicate 215.62 

Andesite 165.62 

Granite 162.62 

Diabase 181.25 

Diorite 171.87 

Slates 165.62 

Sandstones 162.50 

Rhyolite 156.25 


4.79 
7.01 
5.37 
7.19 

10.06 

13.73 

11.80 

3.62 

7.61 

6.21 

8.04 

8.42 

15.09 

4.44 

6.33 

6.53 

8.42 

6.40 

8.31 

2.81 

4.27 

4.81 

6.18 

9.04 

10.66 

11.23 

12.07 

2.35 

3.76 

15.74 

4.35 

4.77 

4.57 

7.90 

7.32 

9.28 

12.07 

12.30 

11.03 

11.63 

12.07 

12.30 

12.80 


The  specific  gravity  of  any  particular  mineral  has  a  considerable  range,  and  a 
medium  has  been  taken.  The  possible  error  is  inconsequential  for  the  purpose  of 
these  calculations. 


16  PRINCIPLES  OF  MINING. 

For  example,  a  representative  gold  ore  may  contain  in  the  main 
96%  quartz,  and  4%  iron  pyrite,  and  the  weight  of  the  ore  may 
be  deduced  as  follows :  — • 

Quartz,          96%  x  12.07  =  11.58 
Iron  Pyrite,    4%  x    6.40  =      .25 

11.83  cubic  feet  per  ton. 

Most  engineers,  to  compensate  porosity,  would  allow  twelve  to 
thirteen  cubic  feet  per  ton. 

CLASSIFICATION   OF   ORE   IN  SIGHT. 

The  risk  in  estimates  of  the  average  value  of  standing  ore  is 
dependent  largely  upon  how  far  values  disclosed  by  sampling 
are  assumed  to  penetrate  beyond  the  tested  face,  and  this  de- 
pends upon  the  geological  character  of  the  deposit.  From 
theoretical  grounds  and  experience,  it  is  known  that  such  values 
will  have  some  extension,  and  the  assumption  of  any  given  dis- 
tance is  a  calculation  of  risk.  The  multiplication  of  develop- 
ment openings  results  in  an  increase  of  sampling  points  available 
and  lessens  the  hazards.  The  frequency  of  such  openings  varies 
in  different  portions  of  every  mine,  and  thus  there  are  inequali- 
ties of  risk.  It  is  therefore  customary  in  giving  estimates  of 
standing  ore  to  classify  the  ore  according  to  the  degree  of  risk 
assumed,  either  by  stating  the  number  of  sides  exposed  or  by 
other  phrases.  Much  discussion  and  ink  have  been  devoted  to 
trying  to  define  what  risk  may  be  taken  in  such  matters,  that  is 
in  reality  how  far  values  may  be  assumed  to  penetrate  into  the 
unbroken  ore.  Still  more  has  been  consumed  in  attempts  to  coin 
terms  and  make  classifications  which  will  indicate  what  ratio  of 
hazard  has  been  taken  in  stating  quantities  and  values. 

The  old  terms  "ore  in  sight"  and  " profit  in  sight"  have  been 
of  late  years  subject  to  much  malediction  on  the  part  of  engineers 
because  these  expressions  have  been  so  badly  abused  by  the 
charlatans  of  mining  in  attempts  to  cover  the  flights  of  their 
imaginations.  A  large  part  of  Volume  X  of  the  "Institution  of 
Mining  and  Metallurgy"  has  been  devoted  to  heaping  infamy  on 


MINE  VALUATION.  17 

these  terms,  yet  not  only  have  they  preserved  their  places  in 
professional  nomenclature,  but  nothing  has  been  found  to  super- 
sede them. 

Some  general  term  is  required  in  daily  practice  to  cover  the 
whole  field  of  visible  ore,  and  if  the  phrase  "ore  in  sight"  be 
defined,  it  will  be  easier  to  teach  the  laymen  its  proper  use  than 
to  abolish  it.  In  fact,  the  substitutes  are  becoming  abused  as 
much  as  the  originals  ever  were.  All  convincing  expressions  will 
be  misused  by  somebody. 

The  legitimate  direction  of  reform  has  been  to  divide  the 
general  term  of  "ore  in  sight"  into  classes,  and  give  them  names 
which  will  indicate  the  variable  amount  of  risk  of  continuity  in 
different  parts  of  the  mine.  As  the  frequency  of  sample  points, 
and  consequently  the  risk  of  continuity,  will  depend  upon  the 
detail  with  which  the  mine  is  cut  into  blocks  by  the  development 
openings,  and  upon  the  number  of  sides  of  such  blocks  which  are 
accessible,  most  classifications  of  the  degree  of  risk  of  continuity 
have  been  defined  in  terms  of  the  number  of  sides  exposed  in  the 
blocks.  Many  phrases  have  been  coined  to  express  such  classi- 
fications; those  most  currently  used  are  the  following:  — 

Positive  Ore  j  Ore  exposed  on  four  sides  in  blocks  of  a  size 
Ore  Developed}  variously  prescribed. 

Ore  Blocked  Out        Ore  exposed  on  three  sides  within  reason- 
able distance  of  each  other. 

Probable  Ore     ]      ~  •  •, 

,     .      \     Ore  exposed  on  two  sides. 
Ore  Developing  j 

Possible  Ore  j  The  whole  or  a  part  of  the  ore  below  the 
Ore  Expectant  J  lowest  level  or  beyond  the  range  of  vision. 

No  two  of  these  parallel  expressions  mean  quite  the  same 
thing;  each  more  or  less  overlies  into  another  class,  and  in  fact 
none  of  them  is  based  upon  a  logical  footing  for  such  a  classifi- 
cation. For  example,  values  can  be  assumed  to  penetrate  some 
distance  from  every  sampled  face,  even  if  it  be  only  ten  feet,  so 
that  ore  exposed  on  one  side  will  show  some  "positive"  or  "de- 
veloped" ore  which,  on  the  lines  laid  down  above,  might  be 


18 


PRINCIPLES   OF  MINING. 


"probable"  or  even  " possible"  ore.  Likewise,  ore  may  be 
"fully  developed"  or  " blocked  out"  so  far  as  it  is  necessary  for 
stoping  purposes  with  modern  wide  intervals  between  levels, 
and  still  be  in  blocks  too  large  to  warrant  an  assumption  of  con- 
tinuity of  values  to  their  centers  (Fig.  1).  As  to  the  third 
class  of  "possible"  ore,  it  conveys  an  impression  of  tangibility 


FIG.  1.  —  Longitudinal  section  of  a  mine,  showing  classification  of  the  exposed  ore. 
Scale,  400  feet  =  1  inch. 

to  a  nebulous  hazard,  and  should  never  be  used  in  connection 
with  positive  tonnages.  This  part  of  the  mine's  value  comes 
under  extension  of  the  deposit  a  long  distance  beyond  openings, 
which  is  a  speculation  and  cannot  be  denned  in  absolute  tons 
without  exhaustive  explanation  of  the  risks  attached,  in  which 
case  any  phrase  intended  to  shorten  description  is  likely  to  be 
misleading. 

Therefore  empirical   expressions  in  terms   of  development 
openings  cannot  be  made  to  cover  a  geologic  factor  such  as  the 


MINE  VALUATION.  19 

distribution  of  metals  through  a  rock  mass.  The  only  logical 
basis  of  ore  classification  for  estimation  purposes  is  one  which 
is  founded  on  the  chances  of  the  values  penetrating  from  the 
surface  of  the  exposures  for  each  particular  mine.  Ore  that  may 
be  calculated  upon  to  a  certainty  is  that  which,  taking  into  con- 
sideration the  character  of  the  deposit,  can  be  said  to  be  so 
sufficiently  surrounded  by  sampled  faces  that  the  distance  into 
the  mass  to  which  values  are  assumed  to  extend  is  reduced  to  a 
minimum  risk.  Ore  so  far  removed  from  the  sampled  face  as  to 
leave  some  doubt,  yet  affording  great  reason  for  expectation  of 
continuity,  is  " probable"  ore.  The  third  class  of  ore  mentioned, 
which  is  that  depending  upon  extension  of  the  deposit  and  in 
which,  as  said  above,  there  is  great  risk,  should  be  treated  sepa- 
rately as  the  speculative  value  of  the  mine.  Some  expressions 
are  desirable  for  these  classifications,  and  the  writer's  own  pref- 
erence is  for  the  following,  with  a  definition  based  upon  the 
controlling  factor  itself. 
They  are:  — 

Proved  Ore  Ore  where  there  is  practically  no  risk  of 

failure  of  continuity. 

Probable  Ore  Ore  where  there  is  some  risk,  yet  warrant- 

able justification  for  assumption  of  con- 
tinuity. 

Prospective  Ore  Ore  which  cannot  be  included  in  the  above 
classes,  nor  definitely  known  or  stated  in 
any  terms  of  tonnage. 

What  extent  of  openings,  and  therefore  of  sample  faces,  is 
required  for  the  ore  to  be  called  " proved"  varies  naturally  with 
the  type  of  deposit,  —  in  fact  with  each  mine.  In  a  general  way, 
a  fair  rule  in  gold  quartz  veins  below  influence  of  secondary 
alteration  is  that  no  point  in  the  block  shall  be  over  fifty  feet 
from  the  points  sampled.  In  limestone  or  andesite  replace- 
ments, as  by  gold  or  lead  or  copper,  the  radius  must  be  less.  In 
defined  lead  and  copper  lodes,  or  in  large  lenticular  bodies  such 
as  the  Tennessee  copper  mines,  the  radius  may  often  be  con- 
siderably greater,  —  say  one  hundred  feet.  In  gold  deposits  of 


'2'2  PRINCIPLES  OF   MlXINtJ. 

able  work  arises  from  his  ability  to  anticipate  in  the  youth 
of  the  mine  the  symptoms  of  its  old  age.  The  work  of  our 
geologic  friends  is,  however,  the  very  foundation  on  which  we 
lay  our  forecasts. 

Geologists  have,  as  the  result  of  long  observation,  propounded 
for  us  certain  hypotheses  which,  while  still  hypotheses,  have 
proved  to  account  so  widely  for  our  underground  experience 
that  no  engineer  can  afford  to  lose  sight  of  them.  Although 
there  is  a  lack  of  safety  in  fixed  theories  as  to  ore  deposition,  and 
although  such  conclusions  cannot  be  translated  into  feet  and 
metal  value,  they  are  nevertheless  useful  weights  on  the  scale 
where  probabilities  are  to  be  weighed. 

A  method  in  vogue  with  many  engineers  is,  where  the  bottom 
level  is  good,  to  assume  the  value  of  the  extension  in  depth  as  a 
sum  proportioned  to  the  profit  in  sight,  and  thus  evade  the  use 
of  geological  evidence.  The  addition  of  various  percentages  to 
the  profit  in  sight  has  been  used  by  engineers,  and  proposed  in 
technical  publications,  as  varying  from  25  to  50%.  That  is, 
they  roughly  assess  the  extension  in  depth  to  be  worth  one-fifth 
to  one-third  of  the  whole  value  of  an  equipped  mine,  ^^hile 
experience  may  have  sometimes  demonstrated  this  to  be  a  prac- 
tical method,  it  certainly  has  little  foundation  in  either  science 
or  logic,  and  the  writer's  experience  is  that  such  estimates  are  un- 
true in  practice.  The  quantity  of  ore  which  may  be  in  sight  is 
largely  the  result  of  managerial  policy.  A  small  mill  on  a  large 
mine,  under  rapid  development,  will  result  in  extensive  ore- 
reserves,  while  a  large  mill  eating  away  rapidly  on  the  same 
mine  under  the  same  scale  of  development  would  leave  small 
reserves.  On  the  above  scheme  of  valuation  the  extension  in 
depth  would  be  worth  very  different  sums,  even  when  the  deep- 
est level  might  be  at  the  same  horizon  in  both  cases.  More- 
over, no  mine  starts  at  the  surface  with  a  large  amount  of  ore 
in  sight.  Yet  as  a  general  rule  this  is  the  period  when  its  ex- 
tension is  most  valuable,  for  when  the  deposit  is  exhausted  to 
2000  feet,  it  is  not  likely  to  have  such  extension  in  depth  as  when 
opened  one  hundred  feet,  no  matter  what  the  ore-reserves  may 
be.  Further,  such  bases  of  valuation  fail  to  take  into  account 


MINE  VALUATION.  23 

the  widely  varying  geologic  character  of  different  mines,  and 
they  disregard  any  collateral  evidence  either  of  continuity  from 
neighboring  development,  or  from  experience  in  the  district. 
Logically,  the  prospective  value  can  be  simply  a  factor  of  how 
far  the  ore  in  the  individual  mine  may  be  expected  to  extend, 
and  not  a  factor  of  the  remnant  of  ore  that  may  still  be  un- 
worked  above  the  lowest  level. 

An  estimation  of  the  chances  of  this  extension  should  be  based 
solely  on  the  local  factors  which  bear  on  such  extension,  and 
these  are  almost  wholly  dependent  upon  the  character  of  the 
deposit.  These  various  geological  factors  from  a  mining  engi- 
neer's point  of  view  are:  — 

1.  The  origin  and  structural  character  of  the  ore-deposit. 

2.  The  position  of  openings  in  relation  to  secondary  alteration. 

3.  The  size  of  the  deposit. 

4.  The  depth  to  which  the  mine  has  already  been  exhausted. 

5.  The  general  experience  of  the  district  for  continuity  and 

the  development  of  adjoining  mines. 

The  Origin  and  Structural  Character  of  the  Deposit.  —  In  a 
general  way,  the  ore-deposits  of  the  order  under  discussion 
originate  primarily  through  the  deposition  of  metals  from  gases 
or  solutions  circulating  along  avenues  in  the  earth's  crust.*  The 
original  source  of  metals  is  a  matter  of  great  disagreement,  and 
does  not  much  concern  the  miner.  To  him,  however,  the  origin 
and  character  of  the  avenue  of  circulation,  the  enclosing  rock, 
the  influence  of  the  rocks  on  the  solution,  and  of  the  solutions 
on  the  rocks,  have  a  great  bearing  on  the  probable  continuity  of 
the  volume  and  value  of  the  ore. 

All  ore-deposits  vary  in  value  and,  in  the  miner's  view,  only 
those  portions  above  the  pay  limit  are  ore-bodies,  or  ore-shoots. 
The  localization  of  values  into  such  pay  areas  in  an  ore-deposit 
are  apparently  influenced  by:  — 

1.  The  distribution  of  the  open  spaces  created  by  structural 
movement,  fissuring,  or  folding  as  at  Bendigo. 

*  The  class  of  magmatic  segregations  is  omitted,  as  not  being  of  suffi- 
ciently frequent  occurrence  in  payable  mines  to  warrant  troubling  with  it 
here. 


22  PRINCIPLES   OF  MINING. 

able  work  arises  from  his  ability  to  anticipate  in  the  youth 
of  the  mine  the  symptoms  of  its  old  age.  The  work  of  our 
geologic  friends  is,  however,  the  very  foundation  on  which  we 
lay  our  forecasts. 

Geologists  have,  as  the  result  of  long  observation,  propounded 
for  us  certain  hypotheses  which,  while  still  hypotheses,  have 
proved  to  account  so  widely  for  our  underground  experience 
that  no  engineer  can  afford  to  lose  sight  of  them.  Although 
there  is  a  lack  of  safety  in  fixed  theories  as  to  ore  deposition,  and 
although  such  conclusions  cannot  be  translated  into  feet  and 
metal  value,  they  are  nevertheless  useful  weights  on  the  scale 
where  probabilities  are  to  be  weighed. 

A  method  in  vogue  with  many  engineers  is,  where  the  bottom 
level  is  good,  to  assume  the  value  of  the  extension  in  depth  as  a 
sum  proportioned  to  the  profit  in  sight,  and  thus  evade  the  use 
of  geological  evidence.  The  addition  of  various  percentages  to 
the  profit  in  sight  has  been  used  by  engineers,  and  proposed  in 
technical  publications,  as  varying  from  25  to  50%.  That  is, 
they  roughly  assess  the  extension  in  depth  to  be  worth  one-fifth 
to  one-third  of  the  whole  value  of  an  equipped  mine.  While 
experience  may  have  sometimes  demonstrated  this  to  be  a  prac- 
tical method,  it  certainly  has  little  foundation  in  either  science 
or  logic,  and  the  writer's  experience  is  that  such  estimates  are  un- 
true in  practice.  The  quantity  of  ore  which  may  be  in  sight  is 
largely  the  result  of  managerial  policy.  A  small  mill  on  a  large 
mine,  under  rapid  development,  will  result  in  extensive  ore- 
reserves,  while  a  large  mill  eating  away  rapidly  on  the  same 
mine  under  the  same  scale  of  development  would  leave  small 
reserves.  On  the  above  scheme  of  valuation  the  extension  in 
depth  would  be  worth  very  different  sums,  even  when  the  deep- 
est level  might  be  at  the  same  horizon  in  both  cases.  More- 
over, no  mine  starts  at  the  surface  with  a  large  amount  of  ore 
in  sight.  Yet  as  a  general  rule  this  is  the  period  when  its  ex- 
tension is  most  valuable,  for  when  the  deposit  is  exhausted  to 
2000  feet,  it  is  not  likely  to  have  such  extension  in  depth  as  when 
opened  one  hundred  feet,  no  matter  what  the  ore-reserves  may 
be.  Further,  such  bases  of  valuation  fail  to  take  into  account 


MINE  VALUATION.  23 

the  widely  varying  geologic  character  of  different  mines,  and 
they  disregard  any  collateral  evidence  either  of  continuity  from 
neighboring  development,  or  from  experience  in  the  district. 
Logically,  the  prospective  value  can  be  simply  a  factor  of  how 
far  the  ore  in  the  individual  mine  may  be  expected  to  extend, 
and  not  a  factor  of  the  remnant  of  ore  that  may  still  be  un- 
worked  above  the  lowest  level. 

An  estimation  of  the  chances  of  this  extension  should  be  based 
solely  on  the  local  factors  which  bear  on  such  extension,  and 
these  are  almost  wholly  dependent  upon  the  character  of  the 
deposit.  These  various  geological  factors  from  a  mining  engi- 
neer's point  of  view  are:  — 

1.  The  origin  and  structural  character  of  the  ore-deposit. 

2.  The  position  of  openings  in  relation  to  secondary  alteration. 

3.  The  size  of  the  deposit. 

4.  The  depth  to  which  the  mine  has  already  been  exhausted. 

5.  The  general  experience  of  the  district  for  continuity  and 

the  development  of  adjoining  mines. 

The  Origin  and  Structural  Character  of  the  Deposit.  —  In  a 

general  way,  the  ore-deposits  of  the  order  under  discussion 
originate  primarily  through  the  deposition  of  metals  from  gases 
or  solutions  circulating  along  avenues  in  the  earth's  crust.*  The 
original  source  of  metals  is  a  matter  of  great  disagreement,  and 
does  not  much  concern  the  miner.  To  him,  however,  the  origin 
and  character  of  the  avenue  of  circulation,  the  enclosing  rock, 
the  influence  of  the  rocks  on  the  solution,  and  of  the  solutions 
on  the  rocks,  have  a  great  bearing  on  the  probable  continuity  of 
the  volume  and  value  of  the  ore. 

All  ore-deposits  vary  in  value  and,  in  the  miner's  view,  only 
those  portions  above  the  pay  limit  are  ore-bodies,  or  ore-shoots. 
The  localization  of  values  into  such  pay  areas  in  an  ore-deposit 
are  apparently  influenced  by :  — 

1.  The  distribution  of  the  open  spaces  created  by  structural 
movement,  fissuring,  or  folding  as  at  Bendigo. 

*  The  class  of  magmatic  segregations  is  omitted,  as  not  being  of  suffi- 
ciently frequent  occurrence  in  payable  mines  to  warrant  troubling  with  it 
here. 


24  PRINCIPLES  OF  MINING. 

2.  The  intersection  of  other  fractures  which,  by  mingling  of 

solutions  from  different  sources,  provided  precipi- 
tating conditions,  as  shown  by  enrichments  at 
cross-veins. 

3.  The  influence  of  the  enclosing  rocks  by:  — 

(a)  Their   solubility,    and   therefore    susceptibility    to 

replacement. 
(6)  Their  influence  as  a  precipitating  agent  on  solutions. 

(c)  Their  influence  as  a  source  of  metal  itself. 

(d)  Their  texture,  in  its  influence  on  the  character  of 

the  fracture.  In  homogeneous  rocks  the  ten- 
dency is  to  open  clean-cut  fissures;  in  friable 
rocks,  zones  of  brecciation;  in  slates  or  schistose 
rocks,  linked  lenticular  open  spaces;  —  these  in- 
fluences exhibiting  themselves  in  miner's  terms 
respectively  in  "  well-defined  fissure  veins/' 
"lodes,"  and  "lenses." 

(e)  The  physical  character  of  the  rock  mass  and  the 

dynamic  forces  brought  to  bear  upon  it.  This 
is  a  difficult  study  into  the  physics  of  stress  in 
cases  of  fracturing,  but  its  local  application  has 
not  been  without  results  of  an  important  order. 

4.  Secondary  alteration  near  the  surface,  more  fully  discussed 

later. 

It  is  evident  enough  that  the  whole  structure  of  the  deposit  is 
a  necessary  study,  and  even  a  digest  of  the  subject  is  not  to  be 
compressed  into  a  few  paragraphs. 

From  the  point  of  view  of  continuity  of  values,  ore-deposits 
may  be  roughly  divided  into  three  classes.     They  are:  — 

1.  Deposits  of  the  infiltration  type  in  porous  beds,  such  as 

Lake  Superior  copper  conglomerates  and  African  gold 
bankets. 

2.  Deposits  of  the  fissure  vein  type,  such  as  California  quartz 

veins. 

3.  Replacement  or  impregnation  deposits  on  the  lines  of  fis- 

suring  or  otherwise. 


MINE  VALUATION.  25 

In  a  general  way,  the  uniformity  of  conditions  of  deposition 
in  the  first  class  has  resulted  in  the  most  satisfactory  continuity 
of  ore  and  of  its  metal  contents.  In  the  second,  depending 
much  upon  the  profundity  of  the  earth  movements  involved,  there 
is  laterally  and  vertically  a  reasonable  basis  for  expectation  of 
continuity  but  through  much  less  distance  than  in  the  first 
class. 

The  third  class  of  deposits  exhibits  widely  different  phenom- 
ena as  to  continuity  and  no  generalization  is  of  any  value.  In 
gold  deposits  of  this  type  in  West  Australia,  Colorado,  and  Ne- 
vada, continuity  far  beyond  a  sampled  face  must  be  received 
with  the  greatest  skepticism.  Much  the  same  may  be  said  of 
most  copper  replacements  in  limestone.  On  the  other  hand  the 
most  phenomenal  regularity  of  values  have  been  shown  in  cer- 
tain Utah  and  Arizona  copper  mines,  the  result  of  secondary  in- 
filtration in  porphyritic  gangues.  The  Mississippi  Valley  lead 
and  zinc  deposits,  while  irregular  in  detail,  show  remarkable  con- 
tinuity by  way  of  reoccurrence  over  wide  areas.  The  estimation 
of  the  prospective  value  of  mines  where  continuity  of  production 
is  dependent  on  reoccurrence  of  ore-bodies  somewhat  propor- 
tional to  the  area,  such  as  these  Mississippi  deposits  or  to  some 
extent  as  in  Cobalt  silver  veins,  is  an  interesting  study,  but  one 
that  offers  little  field  for  generalization. 

The  Position  of  the  Openings  in  Relation  to  Secondary  Al- 
teration. —  The  profound  alteration  of  the  upper  section  of  ore- 
deposits  by  oxidation  due  to  the  action  of  descending  surface 
waters,  and  their  associated  chemical  agencies,  has  been  gener- 
ally recognized  for  a  great  many  years.  Only  recently,  however, 
has  it  been  appreciated  that  this  secondary  alteration  extends 
into  the  sulphide  zone  as  well.  The  bearing  of  the  secondary 
alteration,  both  in  the  oxidized  and  upper  sulphide  zones,  is  of 
the  most  sweeping  economic  character.  In  considering  exten- 
sion of  values  in  depth,  it  demands  the  most  rigorous  investiga- 
tion. Not  only  does  the  metallurgical  character  of  the  ores 
change  with  oxidation,  but  the  complex  reactions  due  to  de- 
scending surface  waters  cause  leaching  and  a  migration  of  met- 
als from  one  horizon  to  another  lower  down,  and  also  in  many 


26  PRINCIPLES  OF  MINING. 

cases  a  redistribution  of  their  sequence  in  the  upper  zones  of 
the  deposit. 

The  effect  of  these  agencies  has  been  so  great  in  many  cases 
as  to  entirely  alter  the  character  of  the  mine  and  extension  in 
depth  has  necessitated  a  complete  reequipment.  For  instance, 
the  Mt.  Morgan  gold  mine,  Queensland,  has  now  become  a  cop- 
per mine;  the  copper  mines  at  Butte  were  formerly  silver 
mines;  Leadville  has  become  largely  a  zinc  producer  instead  of 
lead. 

From  this  alteration  aspect  ore-deposits  may  be  considered 
to  have  four  horizons:  — 

1.  The  zone  near  the  outcrop,  where  the  dominating  feature 

is  oxidation  and  leaching  of  the  soluble  minerals. 

2.  A  lower  horizon,  still  in  the  zone  of  oxidation,  where  the 

predominant  feature  is  the  deposition  of  metals  as  native, 
oxides,  and  carbonates. 

3.  The  upper  horizon  of  the  sulphide  zone,  where  the  special 

feature  is  the  enrichment  due  to  secondary  deposition 
as  sulphides. 

4.  The  region  below  these  zones  of  secondary  alteration,  where 

the  deposit  is  in  its  primary  state. 

These  zones  are  seldom  sharply  defined,  nor  are  they  always 
all  in  evidence.  How  far  they  are  in  evidence  will  depend, 
among  other  things,  upon  the  amount  and  rapidity  of  erosion, 
the  structure  and  mineralogical  character  of  the  deposit,  and 
upon  the  enclosing  rock. 

If  erosion  is  extremely  rapid,  as  in  cold,  wet  climates,  and 
rough  topography,  or  as  in  the  case  of  glaciation  of  the  Lake 
copper  deposits,  denudation  follows  close  on  the  heels  of  altera- 
tion, and  the  surface  is  so  rapidly  removed  that  we  may  have  the 
primary  ore  practically  at  the  surface.  Flat,  arid  regions  pre- 
sent the  other  extreme,  for  denudation  is  much  slower,  and 
conditions  are  most  perfect  for  deep  penetration  of  oxidizing 
agencies,  and  the  consequent  alteration  and  concentration  of 
the  metals. 

The  migration  of  metals  from  the  top  of  the  oxidized  zone 


MINE  VALUATION.  27 

leaves  but  a  barren  cap  for  erosion.  The  consequent  effect 
of  denudation  that  lags  behind  alteration  is  to  raise  slowly  the 
concentrated  metals  toward  the  surface,  and  thus  subject  them 
to  renewed  attack  and  repeated  migration.  In  this  manner  we 
can  account  for  the  enormous  concentration  of  values  in  the  lower 
oxidized  and  upper  sulphide  zones  overlying  very  lean  sulphides 
in  depth. 

Some  minerals  are  more  freely  soluble  and  more  readily 
precipitated  than  others.  From  this  cause  there  is  in  complex 
metal  deposits  a  rearrangement  of  horizontal  sequence,  in  addi- 
tion to  enrichment  at  certain  horizons  and  impoverishment 
at  others.  The  whole  subject  is  one  of  too  great  complexity 
for  adequate  consideration  in  this  discussion.  No  engineer  is 
properly  equipped  to  give  judgment  on  extension  in  depth  with- 
out a  thorough  grasp  of  the  great  principles  laid  down  by  Van 
Hise,  Emmons,  Lindgren,  Weed,  and  others.  We  may,  how- 
ever, briefly  examine  some  of  the  theoretical  effects  of  such 
alteration. 

Zinc,  iron,  and  lead  sulphides  are  a  common  primary  com- 
bination. These  metals  are  rendered  soluble  from  their  usual 
primary  forms  by  oxidizing  agencies,  in  the  order  given.  They 
reprecipitate  as  sulphides  in  the  reverse  sequence.  The  re- 
sult is  the  leaching  of  zinc  and  iron  readily  in  the  oxidized 
zone,  thus  differentially  enriching  the  lead  which  lags  behind, 
and  a  further  extension  of  the  lead  horizon  is  provided  by  the 
early  precipitation  of  such  lead  as  does  migrate.  Therefore, 
the  lead  often  predominates  in  the  second  and  the  upper  portion 
of  the  third  zone,  with  the  zinc  and  iron  below.  Although  the 
action  of  all  surface  waters  is  toward  oxidation  and  carbonation 
of  these  metals,  the  carbonate  development  of  oxidized  zones  is 
more  marked  when  the  enclosing  rocks  are  calcareous. 

In  copper-iron  deposits,  the  comparatively  easy  decomposition 
and  solubility  and  precipitation  of  the  copper  and  some  iron 
salts  generally  result  in  more  extensive  impoverishment  of  these 
metals  near  the  surface,  and  more  predominant  enrichment  at 
a  lower  horizon  than  is  the  case  with  any  other  metals.  The 
barren  "iron  hat"  at  the  first  zone,  the  carbonates  and  oxides 


28  PRINCIPLES  OF  MINING. 

at  the  second,  the  enrichment  with  secondary  copper  sulphides 
at  the  top  of  the  third,  and  the  occurrence  of  secondary  copper- 
iron  sulphides  below,  are  often  most  clearly  defined.  In  the  easy 
recognition  of  the  secondary  copper  sulphides,  chalcocite,  bornite, 
etc.,  the  engineer  finds  a  finger-post  on  the  road  to  extension 
in  depth;  and  the  directions  upon  this  post  are  not  to  be  dis- 
regarded. The  number  of  copper  deposits  enriched  from  un- 
payability  in  the  first  zone  to  a  profitable  character  in  the  next 
two,  and  unpayability  again  in  the  fourth,  is  legion. 

Silver  occurs  most  abundantly  in  combination  with  either 
lead,  copper,  iron,  or  gold.  As  it  resists  oxidation  and  solution 
more  strenuously  than  copper  and  iron,  its  tendency  when  in 
combination  with  them  is  to  lag  behind  in  migration.  There  is 
thus  a  differential  enrichment  of  silver  in  the  upper  two  zones,  due 
to  the  reduction  in  specific  gravity  of  the  ore  by  the  removal  of 
associated  metals.  Silver  does  migrate  somewhat,  however, 
and  as  it  precipitates  more  readily  than  copper,  lead,  zinc,  or  iron, 
its  tendency  when  in  combination  with  them  is  towards  enrich- 
ment above  the  horizons  of  enrichment  of  these  metals.  When 
it  is  in  combination  with  lead  and  zinc,  its  very  ready  precipita- 
tion from  solution  by  the  galena  leaves  it  in  combination  more 
predominantly  with  the  lead.  The  secondary  enrichment  of 
silver  deposits  at  the  top  of  the  sulphide  zone  is  sometimes  a  most 
pronounced  feature,  and  it  seems  to  be  the  explanation  of  the 
origin  of  many  "  bonanzas." 

In  gold  deposits,  the  greater  resistance  to  solubility  of  this 
metal  than  most  of  the  others,  renders  the  phenomena  of 
migration  to  depth  less  marked.  Further  than  this,  migra- 
tion is  often  interfered  with  by  the  more  impervious  quartz 
matrix  of  many  gold  deposits.  Where  gold  is  associated  with 
large  quantities  of  base  metals,  however,  the  leaching  of  the 
latter  in  the  oxidized  zone  leaves  the  ore  differentially  richer, 
and  as  gold  is  also  slightly  soluble,  in  such  cases  the  migration 
of  the  base  metals  does  carry  some  of  the  gold.  In  the  in- 
stance especially  of  impregnation  or  replacement  deposits, 
where  the  matrix  is  easily  permeable,  the  upper  sulphide  zone  is 
distinctly  richer  than  lower  down,  and  this  enrichment  is 


MINE  VALUATION.  29 

accompanied  by  a  considerable  increase  in  sulphides  and 
tellurides.  The  predominant  characteristic  of  alteration  in 
gold  deposits  is,  however,  enrichment  in  the  oxidized  zone  with 
the  maximum  values  near  the  surface.  The  reasons  for  this 
appear  to  be  that  gold  in  its  resistance  to  oxidation  and 
wholesale  migration  gives  opportunities  to  a  sort  of  combined 
mechanical  and  chemical  enrichment. 

In  dry  climates,  especially,  the  gentleness  of  erosion  allows 
of  more  thorough  decomposition  of  the  outcroppings,  and 
a  mechanical  separation  of  the  gold  from  the  detritus.  It 
remains  on  or  near  the  deposit,  ready  to  be  carried  below, 
mechanically  or  otherwise.  In  wet  climates  this  is  less  pro- 
nounced, for  erosion  bears  away  the  croppings  before  such  an 
extensive  decomposition  and  freeing  of  the  gold  particles. 
The  West  Australian  gold  fields  present  an  especially  prominent 
example  of  this  type  of  superficial  enrichment.  During  the  last 
fifteen  years  nearly  eight  hundred  companies  have  been  formed 
for  working  mines  in  this  region.  Although  from  four  hundred 
of  these  high-grade  ore  has  been  produced,  some  thirty-three 
only  have  ever  paid  dividends.  The  great  majority  have  been 
unpayable  below  oxidation,  —  a  distance  of  one  or  two  hundred 
feet.  The  writer's  unvarying  experience  with  gold  is  that  it  is 
richer  in  the  oxidized  zone  than  at  any  point  below.  While 
cases  do  occur  of  gold  deposits  richer  in  the  upper  sulphide  zone 
than  below,  even  the  upper  sulphides  are  usually  poorer  than 
the  oxidized  region.  In  quartz  veins  preeminently,  evidence 
of  enrichment  in  the  third  zone  is  likely  to  be  practically 
absent. 

Tin  ores  present  an  anomaly  among  the  base  metals  under 
discussion,  in  that  the  primary  form  of  this  metal  in  most  work- 
able deposits  is  an  oxide.  Tin  in  this  form  is  most  difficult 
of  solution  from  ground  agencies,  as  witness  the  great  allu- 
vial deposits,  often  of  considerable  geologic  age.  In  conse- 
quence the  phenomena  of  migration  and  enrichment  are  almost 
wholly  absent,  except  such  as  are  due  to  mechanical  penetra- 
tion of  tin  from  surface  decomposition  of  the  matrix  akin  to 
that  described  in  gold  deposits. 


30  PRINCIPLES  OF  MINING. 

In  general,  three  or  four  essential  facts  from  secondary 
alteration  must  be  kept  in  view  when  prognosticating  exten- 
sions. 

Oxidation  usually  alters  treatment  problems,  and  oxi- 
dized ore  of  the  same  grade  as  sulphides  can  often  be 
treated  more  cheaply.  This  is  not  universal.  Low- 
grade  ores  of  lead,  copper,  and  zinc  may  be  treatable 
by  concentration  when  in  the  form  of  sulphides,  and 
may  be  valueless  when  oxidized,  even  though  of  the 
same  grade. 

Copper  ores  generally  show  violent  enrichment  at  the 
base  of  the  oxidized,  and  at  the  top  of  the  sulphide 
zone. 

Lead-zinc  ores  show  lead  enrichment  and  zinc  impover- 
ishment in  the  oxidized  zone  but  have  usually  less  pro- 
nounced enrichment  below  water  level  than  copper. 
The  rearrangement  of  the  metals  by  the  deeper  mi- 
gration of  the  zinc,  also  renders  them  metallurgically 
of  less  value  with  depth. 

Silver  deposits  are  often  differentially  enriched  in  the 
oxidized  zone,  and  at  times  tend  to  concentrate  in 
the  upper  sulphide  zone. 

Gold  deposits  usually  decrease  in  value  from  the  surface 
through  the  whole  of  the  three  alteration  zones. 

Size  of  Deposits.  —  The  proverb  of  a  relation  between 
extension  in  depth  and  size  of  ore-bodies  expresses  one  of  the 
oldest  of  miners'  beliefs.  It  has  some  basis  in  experience, 
especially  in  fissure  veins,  but  has  little  foundation  in  theory 
and  is  applicable  over  but  limited  areas  and  under  limited  con- 
ditions. 

From  a  structural  view,  the  depth  of  fissuring  is  likely  to  be 
more  or  less  in  proportion  to  its  length  and  breadth  and 
therefore  the  volume  of  vein  filling  with  depth  is  likely  to  be 
proportional  to  length  and  width  of  the  fissure.  As  to  the 
distribution  of  values,  if  we  eliminate  the  influence  of  changing 


MINE  VALUATION.  31 

wall  rocks,  or  other  precipitating  agencies  which  often  cause 
the  values  to  arrange  themselves  in  "  floors,"  and  of  secondary 
alteration,  there  may  be  some  reason  to  assume  distribution  of 
values  of  an  extent  equal  vertically  to  that  displayed  horizontally. 
There  is,  as  said,  more  reason  in  experience  for  this  assumption 
than  in  theory.  A  study  of  the  shape  of  a  great  many  ore-shoots 
in  mines  of  fissure  type  indicates  that  when  the  ore-shoots  or 
ore-bodies  are  approaching  vertical  exhaustion  they  do  not  end 
abruptly,  but  gradually  shorten  and  decrease  in  value,  their 
bottom  boundaries  being  more  often  wedge-shaped  than  even 
lenticular.  If  this  could  be  taken  as  the  usual  occurrence,  it 
would  be  possible  (eliminating  the  evident  exceptions  mentioned 
above)  to  state  roughly  that  the  minimum  extension  of  an  ore- 
body  or  ore-shoot  in  depth  below  any  given  horizon  would  be  a 
distance  represented  by  a  radius  equal  to  one-half  its  length. 
By  length  is  not  meant  necessarily  the  length  of  a  horizontal 
section,  but  of  one  at  right  angles  to  the  downward  axis. 

On  these  grounds,  which  have  been  reenforced  by  much 
experience  among  miners,  the  probabilities  of  extension  are 
somewhat  in  proportion  to  the  length  and  width  of  each  ore- 
body.  For  instance,  in  the  A  mine,  with  an  ore-shoot  1000 
feet  long  and  10  feet  wide,  on  its  bottom  level,  the  minimum 
extension  under  this  hypothesis  would  be  a  wedge-shaped  ore- 
body  with  its  deepest  point  500  feet  below  the  lowest  level,  or  a 
minimum  of  say  200,000  tons.  Similarly,  the  B  mine  with  five 
ore-bodies,  each  300  hundred  feet  long  and  10  feet  wide,  ex- 
posed on  its  lowest  level,  would  have  a  minimum  of  five  wedges 
100  feet  deep  at  their  deepest  points,  or  say  50,000  tons. 
This  is  not  proposed  as  a  formula  giving  the  total  amount  of 
extension  in  depth,  but  as  a  sort  of  yardstick  which  has  ex- 
perience behind  it.  This  experience  applies  in  a  much  less 
degree  to  deposits  originating  from  impregnation  along  lines 
of  fissuring  and  not  at  all  to  replacements. 

Development  in  Neighboring  Mines. — Mines  of  a  district 
are  usually  found  under  the  same  geological  conditions,  and 
show  somewhat  the  same  habits  as  to  extension  in  depth  or 
laterally,  and  especially  similar  conduct  of  ore-bodies  and  ore- 


32  PRINCIPLES  OF  MINING. 

shoots.  As  a  practical  criterion,  one  of  the  most  intimate  guides 
is  the  actual  development  in  adjoining  mines.  For  instance,  in 
Kalgoorlie,  the  Great  Boulder  mine  is  (March,  1908)  working 
the  extension  of  Ivanhoe  lodes  at  points  500  feet  below  the 
lowest  level  in  the  Ivanhoe;  likewise,  the  Block  10  lead  mine 
at  Broken  Hill  is  working  the  Central  ore-body  on  the  Central 
boundary  some  350  feet  below  the  Central  workings.  Such 
facts  as  these  must  have  a  bearing  on  assessing  the  downward 
extension. 

Depth  of  Exhaustion.  — All  mines  become  completely 
exhausted  at  some  point  in  depth.  Therefore  the  actual  dis- 
tance to  which  ore  can  be  expected  to  extend  below  the  lowest 
level  grows  less  with  every  deeper  working  horizon.  The  really 
superficial  character  of  ore-deposits,  even  outside  of  the 
region  of  secondaiy  enrichment  is  becoming  every  year  better 
recognized.  The  prospector's  idea  that  "  she  gets  richer  deeper 
down,"  may  have  some  basis  near  the  surface  in  some  metals, 
but  it  is  not  an  idea  which  prevails  in  the  minds  of  engineers 
who  have  to  work  in  depth.  The  writer,  with  some  others, 
prepared  a  list  of  several  hundred  dividend-paying  metal  mines 
of  all  sorts,  extending  over  North  and  South  America,  Austra- 
lasia, England,  and  Africa.  Notes  were  made  as  far  as  possible 
of  the'  depths  at  which  values  gave  out,  and  also  at  which 
dividends  ceased.  Although  by  no  means  a  complete  census, 
the  list  indicated  that  not  6%  of  mines  (outside  banket)  that 
have  yielded  profits,  ever  made  them  from  ore  won  below  2000 
feet.  Of  mines  that  paid  dividends,  80%  did  not  show  profit- 
able value  below  1500  feet,  and  a  sad  majority  died  above  500. 
Failures  at  short  depths  may  be  blamed  upon  secondary  en- 
richment, but  the  majority  that  reached  below  this  influence 
also  gave  out.  The  geological  reason  for  such  general  unseemly 
conduct  is  not  so  evident.  , 

Conclusion.  —  As  a  practical  problem,  the  assessment  of 
prospective  value  is  usually  a  case  of  "cut  and  try."  The 
portion  of  the  capital  to  be  invested,  which  depends  upon  ex- 
tension, will  require  so  many  tons  of  ore  of  the  same  value  as 
that  indicated  by  the  standing  ore,  in  order  to  justify  the  price. 


MINE  VALUATION.  33 

To  produce  this  tonnage  at  the  continued  average  size  of  the 
ore^bodies  will  require  their  extension  in  depth  so  many  feet 
—  or  the  discovery  of  new  ore-bodies  of  a  certain  size.  The 
five  geological  weights  mentioned  above  may  then  be  put  into 
the  scale  and  a  basis  of  judgment  reached. 


CHAPTER  IV. 
MINE  VALUATION  (Continued). 

RECOVERABLE  PERCENTAGE  OF  THE  GROSS  ASSAY  VALUE J  PRICE 
OF  METALS;  COST  OF  PRODUCTION. 

THE  method  of  treatment  for  the  ore  must  be  known  be- 
fore a  mine  can  be  valued,  because  a  knowledge  of  the  recov- 
erable percentage  is  as  important  as  that  of  the  gross  value  of 
the  ore  itself.  The  recoverable  percentage  is  usually  a  factor 
of  working  costs.  Practically  every  ore  can  be  treated  and  all 
the  metal  contents  recovered,  but  the  real  problem  is  to  know 
the  method  and  percentage  of  recovery  which  will  yield  the 
most  remunerative  result,  if  any.  This  limit  to  profitable  re- 
covery regulates  the  amount  of  metal  which  should  be  lost,  and 
the  amount  of  metal  which  consequently  must  be  deducted 
from  the  gross  value  before  the  real  net  value  of  the  ore  can 
be  calculated.  Here,  as  everywhere  else  in  mining,  a  compro- 
mise has  to  be  made  with  nature,  and  we  take  what  we  can  get 
—  profitably.  For  instance,  a  copper  ore  may  be  smelted  and  a 
99%  recovery  obtained.  Under  certain  conditions  this  might 
be  done  at  a  loss,  while  the  same  ore  might  be  concentrated 
before  smelting  and  yield  a  profit  with  a  70%  recovery.  An 
additional  20%  might  be  obtained  by  roasting  and  leaching 
the  residues  from  concentration,  but  this  would  probably 
result  in  an  expenditure  far  greater  than  the  value  of  the  20% 
recovered.  If  the  ore  is  not  already  under  treatment  on  the 
mine,  or  exactly  similar  ore  is  not  under  treatment  elsewhere, 
with  known  results,  the  method  must  be  determined  experi- 
mentally, either  by  the  examining  engineer  or  by  a  special 
metallurgist. 

Where  partially  treated  products,  such  as  concentrates, 
are  to  be  sold,  not  only  will  there  be  further  losses,  but  de- 

34 


MINE  VALUATION.  35 

ductions  will  be  made  by  the  smelter  for  deleterious  metals  and 
other  charges.  All  of  these  factors  must  be  found  out,  —  and 
a  few  sample  smelting  returns  from  a  similar  ore  are  useful. 

To  cover  the  whole  field  of  metallurgy  and  discuss  what 
might  apply,  and  how  it  might  apply,  under  a  hundred  sup- 
posititious conditions  would  be  too  great  a  digression  from  the 
subject  in  hand.  It  is  enough  to  call  attention  here  to  the 
fact  that  the  residues  from  every  treatment  carry  some  metal, 
and  that  this  loss  has  to  be  deducted  from  the  gross  value  of 
the  ore  in  any  calculations  of  net  values. 

PRICE    OF   METALS. 

Unfortunately  for  the  mining  engineer,  not  only  has  he 
to  weigh  the  amount  of  risk  inherent  in  calculations  involved 
in  the  mine  itself,  but  also  that  due  to  fluctuations  in  the 
value  of  metals.  If  the  ore  is  shipped  to  custom  works,  he 
has  to  contemplate  also  variations  in  freights  and  smelting 
charges.  Gold  from  the  mine  valuer's  point  of  view  has  no 
fluctuations.  It  alone  among  the  earth's  products  gives  no 
concern  as  to  the  market  price.  The  price  to  be  taken  for 
all  other  metals  has  to  be  decided  before  the  mine  can  be 
valued.  This  introduces  a  further  speculation  and,  .as  in  all 
calculations  of  probabilities,  amounts  to  an  estimate  of  the 
amount  of  risk.  In  a  free  market  the  law  of  supply  and 
demand  governs  the  value  of  metals  as  it  does  that  of  all 
other  commodities.  So  far,  except  for  tariff  walls  and  smelting 
rings,  there  is  a  free  market  in  the  metals  under  discussion. 

The  demand  for  metals  varies  with  the  unequal  fluctua- 
tions of  the  industrial  tides.  The  sea  of  commercial  activity 
is  subject  to  heavy  storms,  and  the  mine  valuer  is  compelled 
to  serve  as  weather  prophet  on  this  ocean  of  trouble.  High 
prices,  which  are  the  result  of  industrial  booms,  bring 
about  overproduction,  and  the  collapse  of  these  begets  a 
shrinkage  of  demand,  wherein  consequently  the  tide  of 
price  turns  back.  In  mining  for  metals  each  pound  is 
produced  actually  at  a  different  cost.  In  case  of  an  over- 
supply  of  base  metals  the  price  will  fall  until  it  has  reached 


36  PRINCIPLES  OF  MINING. 

a  point  where  a  portion  of  the  production  is  no  longer  prof- 
itable) and  the  equilibrium  is  established  through  decline 
in  output.  However,  in  the  backward  swing,  due  to  lingering 
overproduction,  prices  usually  fall  lower  than  the  cost  of  pro- 
ducing even  a  much-diminished  supply.  There  is  at  this  point 
what  we  may  call  the  " basic"  price,  that  at  which  pro- 
duction is  insufficient  and  the  price  rises  again.  The  basic 
price  which  is  due  to  this  undue  backward  swing  is  no  more 
the  real  price  of  the  metal  to  be  contemplated  over  so  long 
a  term  of  years  than  is  the  highest  price.  At  how  much  above 
the  basic  price  of  depressed  times  the  product  can  be  safely 
expected  to  find  a  market  is  the  real  question.  Few  mines 
can  be  bought  or  valued  at  this  basic  price.  An  indication 
of  what  this  is  can  be  gained  from  a  study  of  fluctuations  over 
a  long  term  of  years. 

It  is  common  to  hear  the  average  price  over  an  extended 
period  considered  the  " normal"  price,  but  this  basis  for  value 
is  one  which  must  be  used  with  discretion,  for  it  is  not  the 
whole  question  when  mining.  The  "normal"  price  is  the 
average  price  over  a  long  term.  The  lives  of  mines,  and 
especially  ore  in  sight,  may  not  necessarily  enjoy  the  period 
of  this  " normal"  price.  The  engineer  must  balance  his 
judgments  by  the  immediate  outlook  of  the  industrial  weather. 
When  lead  was  falling  steadily  in  December,  1907,  no  engineer 
would  accept  the  price  of  that  date,  although  it  was  then  below 
"normal  " ;  his  product  might  go  to  market  even  lower  yet. 

It  is  desirable  to  ascertain  what  the  basic  and  normal 
prices  are,  for  between  them  lies  safety.  Since  1884  there 
have  been  three  cycles  of  commercial  expansion  and  contrac- 
tion. If  the  average  prices  are  taken  for  these  three  cycles 
separately  (1885-95,  1895-1902,  1902-08)  it  will  be  seen  that 
there  has  been  a  steady  advance  in  prices.  For  the  succeeding 
cycles  lead  on  the  London  Exchange,*  the  freest  of  the  world's 

*  All  London  prices  are  based  on  the  long  ton  of  2,240  Ibs.  Much 
confusion  exists  in  the  copper  trade  as  to  the  classification  of  the  metal. 
New  York  prices  are  quoted  in  electrolytic  and  "Lake";  London's  in 
"Standard."  "  Standard  "  has  now  become  practically  an  arbitrary  term 
peculiar  to  London,  for  the  great  bulk  of  copper  dealt  in  is  "  electrolytic  " 
valued  considerably  over  "  Standard." 


MINE  VALUATION. 


37 


markets  was  £12  12s.  4d.,  £13  3s.  Id.,  and  £17  7s.  Od. 
respectively;  zinc,  £17  14s.  lOd,  £19  3s.  Sd.,  and  £23  3s. 
Od.;  and  standard  copper,  £48  16s.  Od,  £59  10s.  Qd.,  and 
£65  7s.  Qd.  It  seems,  therefore,  that  a  higher  standard  of 
prices  can  be  assumed  as  the  basic  and  normal  than  would 
be  indicated  if  the  general  average  of,  say,  twenty  years  were 
taken.  During  this  period,  the  world's  gold  output  has  nearly 
quadrupled,  and,  whether  the  quantitative  theory  of  gold  be 
accepted  or  not,  it  cannot  be  denied  that  there  has  been  a 
steady  increase  in  the  price  of  commodities.  In  all  base-metal 
mining  it  is  well  to  remember  that  the  production  of  these 
metals  is  liable  to  great  stimulus  at  times  from  the  discovery 
of  new  deposits  or  new  processes  of  recovery  from  hitherto 
unprofitable  ores.  It  is  therefore  for  this  reason  hazardous 
in  the  extreme  to  prophesy  what  prices  will  be  far  in  the 
future,  even  when  the  industrial  weather  is  clear.  But  some 
basis  must  be  arrived  at,  and  from  the  available  outlook  it 
would  seem  that  the  following  metal  prices  are  justifiable  for 
some  time  to  come,  provided  the  present  tariff  schedules  are 
maintained  in  the  United  States: 


LEAD 

SPELTER 

COPPER 

TIN 

SILVER 

London 
Ton 

N.Y. 
Pound 

Lon. 
Ton 

N.Y. 

Pound 

Lon. 
Ton 

N.Y. 

Pound 

Lon. 
Ton 

N.Y. 
Pound 

Lon. 
Per  oz. 

N.Y. 
Per  oz. 

Basic  Price 

£11. 

$.035 

£17 

$.040 

£52 

$.115 

£100 

$.220 

22rf. 

$.44 

Normal  Price 

13.5 

.043 

21 

.050 

65 

.140 

130 

.290 

26 

.52 

In  these  figures  the  writer  has  not  followed  strict  averages, 
but  has  taken  the  general  outlook  combined  with  the  previous 
records.  The  likelihood  of  higher  prices  for  lead  is  mgre 
encouraging  than  for  any  other  metal,  as  no  new  deposits  of 
importance  have  come  forward  for  years,  and  the  old  mines 
are  reaching  considerable  depths.  Nor  does  the  frenzied 
prospecting  of  the  world's  surface  during  the  past  ten  years 
appear  to  forecast  any  very  disturbing  developments.  The 
zinc  future  is  not  so  bright,  for  metallurgy  has  done  wonders 


38  PRINCIPLES  OF  MINING. 

in  providing  methods  of  saving  the  zinc  formerly  discarded 
from  lead  ores,  and  enormous  supplies  will  come  forward  when 
required.  The  tin  outlook  is  encouraging,  for  the  supply 
from  a  mining  point  of  view  seems  unlikely  to  more  than 
keep  pace  with  the  world's  needs.  In  copper  the  demand 
is  growing  prodigiously,  but  the  supplies  of  copper  ores  and 
the  number  of  copper  mines  that  are  ready  to  produce 
whenever  normal  prices  recur  was  never  so  great  as  to-day. 
One  very  hopeful  fact  can  be  deduced  for  the  comfort  of  the 
base  metal  mining  industry  as  a  whole.  If  the  growth  of 
demand  continues  through  the  next  thirty  years  in  the  ratio 
of  the  past  three  decades,  the  annual  demand  for  copper  will 
be  over  3,000,000  tons,  of  lead  over  1,800,000  tons,  of  spelter 
2,800,000  tons,  of  tin  250,000  tons.  Where  such  stupendous 
amounts  of  these  metals  are  to  come  from  at  the  present 
range  of  prices,  and  even  with  reduced  costs  of  production, 
is  far  beyond  any  apparent  source  of  supply.  The  out- 
look for  silver  prices  is  in  the  long  run  not  bright.  As  the 
major  portion  of  the  silver  produced  is  a  bye  product  from 
base  metals,  any  increase  in  the  latter  will  increase  the  silver 
production  despite  very  much  lower  prices  for  the  precious 
metal.  In  the  meantime  the  gradual  conversion  of  all  nations 
to  the  gold  standard  seems  a  matter  of  certainty.  Further, 
silver  may  yet  be  abandoned  as  a  subsidiary  coinage  inasmuch 
as  it  has  now  but  a  token  value  in  gold  standard  countries  if 
denuded  of  sentiment. 

COST    OF   PRODUCTION. 

It  is  hardly  necessary  to  argue  the  relative  importance 
of  the  determination  of  the  cost  of  production  and  the  deter- 
mination of  the  recoverable  contents  of  the  ore.  Obviously, 
the  aim  of  mine  valuation  is  to  know  the  profits  to  be  won, 
and  the  profit  is  the  value  of  the  metal  won,  less  the  cost  of 
production. 

The  cost  of  production  embraces  development,  mining, 
treatment,  management.  Further  than  this,  it  is  often  con- 
tended that,  as  the  capital  expended  in  purchase  and  equip- 


MINE  VALUATION.  39 

ment  must  be  redeemed  within  the  life  of  the  mine,  this  item 
should  also  be  included  in  production  costs.  It  is  true  that 
mills,  smelters,  shafts,  and  all  the  paraphernalia  of  a  mine 
are  of  virtually  negligible  value  when  it  is  exhausted ;  and  that 
all  mines  are  exhausted  sometime  and  every  ton  taken  out 
contributes  to  that  exhaustion ;  and  that  every  ton  of  ore  must 
bear  its  contribution  to  the  return  of  the  investment,  as  well 
as  profit  upon  it.  Therefore  it  may  well  be  said  that  the  re- 
demption of  the  capital  and  its  interest  should  be  considered 
in  costs  per  ton.  The  difficulty  in  dealing  with  the  subject 
from  the  point  of  view  of  production  cost  arises  from  the  fact 
that,  except  possibly  in  the  case  of  banket  gold  and  some 
conglomerate  copper  mines,  the  life  of  a  metal  mine  is  unknown 
beyond  the  time  required  to  exhaust  the  ore  reserves.  The 
visible  life  at  the  time  of  purchase  or  equipment  may  be  only 
three  or  four  years,  yet  the  average  equipment  has  a  longer 
life  than  this,  and  the  anticipation  for  every  mine  is  also 
for  longer  duration  than  the  bare  ore  in  sight.  For  clarity 
of  conclusions  in  mine  valuation  the  most  advisable  course 
is  to  determine  the  profit  in  sight  irrespective  of  capital  re- 
demption in  the  first  instance.  The  questions  of  capital 
redemption,  purchase  price,  or  equipment  cost  can  then  be 
weighed  against  the  margin  of  profit.  One  phase  of  redemp- 
tion will  be  further  discussed  under  " Amortization  of  Capital'' 
and  " Ratio  of  Output  to  the  Mine." 

The  cost  of  production  depends  upon  many  things,  such  as 
the  cost  of  labor,  supplies,  the  size  of  the  ore-body,  the  treat- 
ment necessary,  the  volume  of  output,  etc.;  and  to  discuss 
them  all  would  lead  into  a  wilderness  of  supposititious  cases.  If 
the  mine  is  a  going  concern,  from  which  reliable  data  can  be 
obtained,  the  problem  is  much  simplified.  If  it  is  virgin,  the 
experience  of  other  mines  in  the  same  region  is  the  next  resource; 
where  no  such  data  can  be  had,  the  engineer  must  fall  back 
upon  the  experience  with  mines  still  farther  afield.  Use  is 
sometimes  made  of  the  " comparison  ton"  in  calculating  costs 
upon  mines  where  data  of  actual  experience  are  not  available.  As 
costs  will  depend  in  the  main  upon  items  mentioned  above,  if  the 


40  PRINCIPLES  OF  MINING. 

known  costs  of  a  going  mine  elsewhere  be  taken  as  a  basis,  and 
subtractions .  and  additions  made  for  more  unfavorable  or  favor- 
able effect  of  the  differences  in  the  above  items,  a  fairly  close 
result  can  be  approximated. 

Mine  examinations  are  very  often  inspired  by  the  belief  that 
extended  operations  or  new  metallurgical  applications  to  the 
mine  will  expand  the  profits.  In  such  cases  the  paramount 
questions  are  the  reduction  of  costs  by  better  plant,  larger  out- 
puts, new  processes,  or  alteration  of  metallurgical  basis  and 
better  methods.  If  every  item  of  previous  expenditure  be  gone 
over  and  considered,  together  with  the  equipment,  and  method 
by  which  it  was  obtained,  the  possible  savings  can  be  fairly  well 
deduced,  and  justification  for  any  particular  line  of  action 
determined.  One  view  of  this  subject  will  be  further  discussed 
under  "Ratio  of  Output  to  the  Mine."  The  conditions  which 
govern  the  working  costs  are  on  every  mine  so  special  to  itself, 
that  no  amount  of  advice  is  very  useful.  Volumes  of  advice 
have  been  published  on  the  subject,  but  in  the  main  their 
burden  is  not  to  underestimate. 

In  considering  the  working  costs  of  base-metal  mines,  much 
depends  upon  the  opportunity  for  treatment  in  customs  works, 
smelters,  etc.  Such  treatment  means  a  saving  of  a  large  por- 
tion of  equipment  cost,  and  therefore  of  the  capital  to  be  in- 
vested and  subsequently  recovered.  The  economics  of  home 
treatment  must  be  weighed  against  the  sum  which  would  need 
to  be  set  aside  for  redemption  of  the  plant,  and  unless  there  is  a 
very  distinct  advantage  to  be  had  by  the  former,  no  risks  should 
be  taken.  More  engineers  go  wrong  by  the  erection  of  treatment 
works  where  other  treatment  facilities  are  available,  than  do  so 
by  continued  shipping.  There  are  many  mines  where  the  cost 
of  equipment  could  never  be  returned,  and  which  would  be  value- 
less unless  the  ore  could  be  shipped.  Another  phase  of  foreign 
treatment  arises  from  the  necessity  or  advantage  of  a  mixture  of 
ores,  —  the  opportunity  of  such  mixtures  often  gives  the  public 
smelter  an  advantage  in  treatment  with  which  treatment  on  the 
mine  could  never  compete. 

Fluctuation  in  the  price  of  base  metals  is  a  factor  so  much  to 


MINE  VALUATION.  41 

be  taken  into  consideration,  that  it  is  desirable  in  estimating 
mine  values  to  reduce  the  working  costs  to  a  basis  of  a  "  per  unit " 
of  finished  metal.  This  method  has  the  great  advantage  of  in- 
dicating so  simply  the  involved  risks  of  changing  prices  that 
whoso  runs  may  read.  Where  one  metal  predominates  over  the 
other  to  such  an  extent  as  to  form  the  " backbone"  of  the  value, 
of  the  mine,  the  value  of  the  subsidiary  metals  is  often  deducted 
from  the  cost  of  the  principal  metal,  in  order  to  indicate  more 
plainly  the  varying  value  of  the  mine  with  the  fluctuating  prices 
of  the  predominant  metal.  For  example,  it  is  usual  to  state 
that  the  cost  of  copper  production  from  a  given  ore  will  be  so 
many  cents  per  pound,  or  so  many  pounds  sterling  per  ton. 
Knowing  the  total  metal  extractable  from  the  ore  in  sight,  the 
profits  at  given  prices  of  metal  can  be  readily  deduced.  The 
point  at  which  such  calculation  departs  from  the  aper-ton-of- 
ore"  unto  the  per-unit-cost-of -metal  basis,  usually  lies  at  the 
point  in  ore  dressing  where  it  is  ready  for  the  smelter.  To  take 
a  simple  case  of  a  lead  ore  averaging  20% :  this  is  to  be  first  con- 
centrated and  the  lead  reduced  to  a  concentrate  averaging  70% 
and  showing  a  recovery  of  75%  of  the  total  metal  content.  The 
cost  per  ton  of  development,  mining,  concentration,  manage- 
ment, is  to  this  point  say  $4  per  ton  of  original  crude  ore.  The 
smelter  buys  the  concentrate  for  95%  of  the  value  of  the  metal, 
less  the  smelting  charge  of  $15  per  ton,  or  there  is  a  working  cost 
of  a  similar  sum  by  home  equipment.  In  this  case  4.66  tons  of 
ore  are  required  to  produce  one  ton  of  concentrates,  and  there- 
fore each  ton  of  concentrates  costs  $18.64.  This  amount,  added 
to  the  smelting  charge,  gives  a  total  of  $33.64  for  the  creation  of 
70%  of  one  ton  of  finished  lead,  or  equal  to  2.40  cents  per 
pound  which  can  be  compared  with  the  market  price  less  5%. 
If  the  ore  were  to  contain  20  ounces  of  silver  per  ton,  of  which 
15  ounces  were  recovered  into  the  leady  concentrates,  and  the 
smelter  price  for  the  silver  were  50  cents  per  ounce,  then  the  $7.50 
thus  recovered  would  be  subtracted  from  $33.64,  making  the 
apparent  cost  of  the  lead  1.86  cents  per  pound. 


CHAPTER  V. 
MINE  VALUATION  (Continued). 

REDEMPTION  OR  AMORTIZATION   OF   CAPITAL  AND   INTEREST. 

IT  is  desirable  to  state  in  some  detail  the  theory  of  amortiza- 
tion before  consideration  of  its  application  in  mine  valuation. 

As  every  mine  has  a  limited  life,  the  capital  invested  in  it 
must  be  redeemed  during  the  life  of  the  mine.  It  is  not  suffi- 
cient that  there  be  a  bare  profit  over  working  costs.  In  this 
particular,  mines  differ  wholly  from  many  other  types  of  invest- 
ment, such  as  railways.  In  the  latter,  if  proper  appropriation  is 
made  for  maintenance,  the  total  income  to  the  investor  can  be 
considered  as  interest  or  profit ;  but  in  mines,  a  portion  of  the 
annual  income  must  be  considered  as  a  return  of  capital.  There- 
fore, before  the  yield  on  a  mine  investment  can  be  determined,  a 
portion  of  the  annual  earnings  must  be  set  aside  in  such  a  manner 
that  when  the  mine  is  exhausted  the  original  investment  will  have 
been  restored.  If  we  consider  the  date  due  for  the  return  of  the 
capital  as  the  time  when  the  mine  is  exhausted,  we  may  consider 
the  annual  instalments  as  payments  before  the  due  date,  and  they 
can  be  put  out  at  compound  interest  until  the  time  for  restora- 
tion arrives.  If  they  be  invested  in  safe  securities  at  the  usual 
rate  of  about  4%,  the  addition  of  this  amount  of  compound  in- 
terest will  assist  in  the  repayment  of  the  capital  at  the  due  date, 
so  that  the  annual  contributions  to  a  sinking  fund  need  not 
themselves  aggregate  the  total  capital  to  be  restored,  but  may 
be  smaller  by  the  deficiency  which  will  be  made  up  by  their 
interest  earnings.  Such  a  system  of  redemption  of  capital  is 
called  "  Amortization." 

Obviously  it  is  not  sufficient  for  the  mine  investor  that  his 
capital  shall  have  been  restored,  but  there  is  required  an  excess 
earning  over  and  above  the  necessities  of  this  annual  funding  of 

42 


MINE  VALUATION.  43 

capital.  What  rate  of  excess  return  the  mine  must  yield  is  a  mat- 
ter of  the  risks  in  the  venture  and  the  demands  of  the  investor. 
Mining  business  is  one  where  7%  above  provision  for  capital 
return  is  an  absolute  minimum  demanded  by  the  risks  inherent 
in  mines,  even  where  the  profit  in  sight  gives  warranty  to  the 
return  of  capital.  Where  the  profit  in  sight  (which  is  the  only 
real  guarantee  in  mine  investment)  is  below  the  price  of  the  in- 
vestment, the  annual  return  should  increase  in  proportion. 
There  are  thus  two  distinct  directions  in  which  interest  must  be 
computed,  —  first,  the  internal  influence  of  interest  in  the  amor- 
tization of  the  capital,  and  second,  the  percentage  return  upon 
the  whole  investment  after  providing  for  capital  return. 

There  are  many  limitations  to  the  introduction  of  such  refine- 
ments as  interest  calculations  in  mine  valuation.  It  is  a  sub- 
ject not  easy  to  discuss  with  finality,  for  not  only  is  the  term  of 
years  unknown,  but,  of  more  importance,  there  are  many  factors 
of  a  highly  speculative  order  to  be  considered  in  valuing.  It 
may  be  said  that  a  certain  life  is  known  in  any  case  from  the 
profit  in  sight,  and  that  in  calculating  this  profit  a  deduction 
should  be  made  from  the  gross  profit  for  loss  of  interest  on 
it  pending  recovery.  This  is  true,  but  as  mines  are  seldom 
dealt  with  on  the  basis  of  profit  in  sight  alone,  and  as  the  pur- 
chase price  includes  usually  some  proportion  for  extension  in 
depth,  an  unknown  factor  is  introduced  which  outweighs  the 
known  quantities.  Therefore  the  application  of  the  culmina- 
tive  effect  of  interest  accumulations  is  much  dependent  upon 
the  sort  of  mine  under  consideration.  In  most  cases  of  uncer- 
tain continuity  in  depth  it  introduces  a  mathematical  refine- 
ment not  warranted  by  the  speculative  elements.  For  instance, 
in  a  mine  where  the  whole  value  is  dependent  upon  extension  of 
the  deposit  beyond  openings,  and  where  an  expected  return  of 
at  least  50%  per  annum  is  required  to  warrant  the  risk,  such  re- 
finement would  be  absurd.  On  the  other  hand,  in  a  Witwaters- 
rand  gold  mine,  in  gold  and  tin  gravels,  or  in  massive  copper 
mines  such  as  Bingham  and  Lake  Superior,  where  at  least  some 
sort  of  life  can  be  approximated,  it  becomes  a  most  vital  element 
in  valuation. 


44  PRINCIPLES  OF  MINING. 

In  general  it  may  be  said  that  the  lower  the  total  annual 
return  expected  upon  the  capital  invested,  the  greater  does  the 
amount  demanded  for  amortization  become  in  proportion  to 
this  total  income,  and  therefore  the  greater  need  of  its  intro- 
duction in  calculations.  Especially  is  this  so  where  the  cost  of 
equipment  is  large  proportionately  to  the  annual  return.  Fur- 
ther, it  may  be  said  that  such  calculations  are  of  decreasing  use 
with  increasing  proportion  of  speculative  elements  in  the  price 
of  the  mine.  The  risk  of  extension  in  depth,  of  the  price  of 
metal,  etc.,  may  so  outweigh  the  comparatively  minor  factors 
here  introduced  as  to  render  them  useless  of  attention. 

In  the  practical  conduct  of  mines  or  mining  companies, 
sinking  funds  for  amortization  of  capital  are  never  established. 
In  the  vast  majority  of  mines  of  the  class  under  discussion,  the 
ultimate  duration  of  life  is  unknown,  and  therefore  there  is  no 
basis  upon  which  to  formulate  such  a  definite  financial  policy 
even  were  it  desired.  Were  it  possible  to  arrive  at  the  annual 
sum  to  be  set  aside,  the  stockholders  of  the  mining  type  would 
prefer  to  do  their  own  reinvestment.  The  purpose  of  these  cal- 
culations does  not  lie  in  the  application  of  amortization  to  ad- 
ministrative finance.  It  is  nevertheless  one  of  the  touchstones 
in  the  valuation  of  certain  mines  or  mining  investments.  That 
is,  by  a  sort  of  inversion  such  calculations  can  be  made  to  serve 
as  a  means  to  expose  the  amount  of  risk,  —  to  furnish  a  yard- 
stick for  measuring  the  amount  of  risk  in  the  very  speculations 
of  extension  in  depth  and  price  of  metals  which  attach  to  a  mine. 
Given  the  annual  income  being  received,  or  expected,  the  prob- 
lem can  be  formulated  into  the  determination  of  how  many  years 
it  must  be  continued  in  order  to  amortize  the  investment  and 
pay  a  given  rate  of  profit.  A  certain  length  of  life  is  evident  from 
the  ore  in  sight,  which  may  be  called  the  life  in  sight.  If  the 
term  of  years  required  to  redeem  the  capital  and  pay  an  interest 
upon  it  is  greater  than  the  life  in  sight,  then  this  extended  life 
must  come  from  extension  in  depth,  or  ore  from  other  direction, 
or  increased  price  of  metals.  If  we  then  take  the  volume  and 
profit  on  the  ore  as  disclosed  we  can  calculate  the  number  of 
feet  the  deposit  must  extend  in  depth,  or  additional  tonnage 


MINE  VALUATION.  45 

that  must  be  obtained  of  the  same  grade,  or  the  different  prices 
of  metal  that  must  be  secured,  in  order  to  satisfy  the  demanded 
term  of  years.  These  demands  in  actual  measure  of  ore  or  feet 
or  higher  price  can  then  be  weighed  against  the  geological  and 
industrial  probabilities. 

The  following  tables  and  examples  may  be  of  assistance  in 
these  calculations. 

Table  I.  To  apply  this  table,  the  amount  of  annual  income 
or  dividend  and  the  term  of  years  it  will  last  must  be  known  or 
estimated  factors.  It  is  then  possible  to  determine  the  present 
value  of  this  annual  income  after  providing  for  amortization  and 
interest  on  the  investment  at  various  rates  given,  by  multiplying 
the  annual  income  by  the  factor  set  out. 

A  simple  illustration  would  be  that  of  a  mine  earning  a  profit 
of  $200,000  annually,  and  having  a  total  of  1,000,000  tons  in 
sight,  yielding  a  profit  of  $2  a  ton,  or  a  total  profit  in  sight  of 
$2,000,000,  thus  recoverable  in  ten  years.  On  a  basis  of  a  7% 
return  on  the  investment  and  amortization  of  capital  (Table  I), 
the  factor  is  6.52  x  $200,000  =  $1,304,000  as  the  present  value 
of  the  gross  profits  exposed.  That  is,  this  sum  of  $1,304,000,  if 
paid  for  the  mine,  would  be  repaid  out  of  the  profit  in  sight, 
together  with  7%  interest  if  the  annual  payments  into  sinking 
fund  earn  4%. 


46 


PRINCIPLES   OF  MINING. 


TABLE  I. 

PRESENT  VALUE  OF  AN  ANNUAL    DIVIDEND  OVER  —  YEARS  AT  — °/fl 
AND  REPLACING  CAPITAL  BY  REINVESTMENT  OF  AN  ANNUAL  SUM  AT  4%. 


YEARS 

5% 

6% 

T% 

s% 

9% 

10% 

1 

.95 

.94 

.93 

.92 

.92 

.91 

2 

1.85 

1.82 

1.78 

1.75 

1.72 

1.69 

3 

2.70 

2.63 

2.56 

2.50 

2.44 

2.38 

4 

3.50 

3.38 

3.27 

3.17 

3.07 

2.98 

5 

4.26 

4.09 

3.93 

8.79 

3.64 

3.51 

6 

4.98 

4.74 

4.53 

4.33 

4.15 

3.99 

7 

5.66 

5.36 

5.09 

4.84 

4.62 

4.41 

8 

6.31 

5.93 

5.60 

5.30 

5.04 

4.79 

9 

6.92 

•      6.47 

6.08 

5.73 

5.42 

5.14 

10 

7.50 

6.98 

6.52 

6.12 

5.77 

5.45 

11 

8.05 

7.45 

6.94 

6.49 

6.09 

5.74 

12 

8.58 

7.90 

7.32 

6.82 

6.39 

6.00 

13 

9.08 

8.32 

7.68 

7.13 

6.66 

6.24 

14 

9.55 

8.72 

8.02 

7.42 

6.91 

6.46 

15 

10.00 

9.09 

8.34 

7.79 

7.14 

6.67 

16 

10.43 

9.45 

8.63 

7.95 

7.36 

6.86 

17 

10.85 

9.78 

8.91 

8.18 

7.56 

7.03 

18 

11.24 

10.10 

9.17 

8.40 

7.75 

7.19 

19 

11.61 

10.40 

9.42 

8.61 

7.93 

7.34 

20 

11.96 

10.68 

9.65 

8.80 

8.09 

7.49 

21 

12.30 

10.95 

9.87 

8.99 

8.24 

7.62 

22 

12.62 

11.21 

10.08 

9.16 

8.39 

7.74 

23 

12.93 

11.45 

10.28 

9.32 

8.52 

7.85 

24 

13.23 

11.68 

10.46 

9.47 

8.65 

7.96 

25 

13.51 

11.90 

10.64 

9.61 

8.77 

8.06 

26 

13.78 

12.11 

10.80 

9.75 

8.88 

8.16 

27 

14.04 

12.31 

10.96 

9.88 

8.99 

8.25 

28 

14.28 

12.50 

11.11 

10.00 

9.09 

8.33 

29 

14.52 

12.68 

11.25 

10.11 

9.18 

8.41 

30 

14.74 

12.85 

11.38 

10.22 

9.27 

8.49 

31 

14.96 

13.01 

11.51 

10.32 

9.36 

8.56 

32 

15.16 

13.17 

11.63 

10.42 

9.44 

8.62 

33 

15.36     - 

13.31 

11.75 

10.51 

9.51 

8.69 

34 

15.55 

13.46 

11.86 

10.60 

9.59 

8.75 

35 

15.73 

13.59 

11.96 

10.67 

9.65 

8.80 

36 

15.90 

13.72 

12.06 

10.76 

9.72 

8.86 

37 

16.07 

13.84 

12.16 

10.84 

9.78 

8.91 

38 

16.22 

13.96 

12.25 

10.91 

9.84 

8.96 

39 

16.38 

14.07 

12.34 

10.98 

9.89 

9.00 

40 

16.52 

14.18 

12.42 

11.05 

9.95 

9.05 

Condensed  from  Inwood's  Tables. 


MINE  VALUATION. 


47 


Table  II  is  practically  a  compound  discount  table.  That  is, 
by  it  can  be  determined  the  present  value  of  a  fixed  sum  payable 
at  the  end  of  a  given  term  of  years,  interest  being  discounted  at 
various  given  rates.  Its  use  may  be  illustrated  by  continuing 

the  example  preceding. 

TABLE  II. 

PRESENT  VALUE  OF  $1,  or  £1,  PAYABLE  IN  —  YEARS,  INTEREST  TAKEN 

AT  —  %. 


YEARS 

4% 

6% 

6% 

7% 

1 

.961 

.952 

.943 

.934 

2 

.924 

.907 

.890 

.873 

3 

.889 

.864 

.840 

.816 

4 

.854 

.823 

.792 

.763 

5 

.821 

.783 

.747 

.713 

6 

.790 

.746 

.705 

.666 

7 

.760 

.711 

.665 

.623 

8 

.731 

.677 

.627 

.582 

9 

.702 

.615 

.592 

.544 

10 

.675 

.614 

.558 

.508 

11 

.649 

.585 

.527 

.475 

12 

.625 

.557 

.497 

.444 

18 

.600 

.530 

.469 

.415 

14 

.577 

.505 

.442 

.388 

15 

.555 

.481 

.417 

.362 

16 

.534 

.458  - 

.394 

.339 

17 

.513 

.436 

.371 

.316 

18 

.494- 

.415 

.350 

.296 

19 

.475 

.396 

.330 

.276 

20 

.456 

.377 

.311 

.258 

21 

.439 

.359 

.294 

.241 

22 

.422 

.342 

.277 

.266 

23 

.406 

.325 

.262 

.211 

24 

.390 

.310 

.247 

.197 

25 

.375 

.295 

.233 

.184 

26 

.361 

.281 

.220 

.172 

27 

.347 

.268 

.207 

.161 

28 

.333 

.255 

.196 

.150 

29 

.321 

.243 

.184 

.140 

30 

.308 

.231 

.174 

.131 

31 

.296 

.220 

.164 

.123 

32 

.285 

.210 

.155 

.115 

33 

.274 

.200 

.146 

.107 

34 

.263 

.190 

.138 

.100 

35 

.253 

.181 

.130 

.094 

36 

.244 

.172 

.123 

.087 

37 

.234 

.164 

.116 

.082 

38 

.225 

.156 

.109 

.076 

39 

.216 

.149 

.103 

.071 

40 

.208 

.142 

.097 

.067 

Condensed  from  Inwood's  Tables. 


48 


PRINCIPLES  OF  MINING. 


If  such  a  mine  is  not  equipped,  and  it  is  assumed  that  $200,000 
are  required  to  equip  the  mine,  and  that  two  years  are  required 
for  this  equipment,  the  value  of  the  ore  in  sight  is  still  less,  be- 
cause of  the  further  loss  of  interest  in  delay  and  the  cost  of 
equipment.  In  this  case  the  present  value  of  $1,304,000  in  two 
years,  interest  at  7%,  the  factor  is  .87  x  1,304,000  =$1,134,480. 
From  this  comes  off  the  cost  of  equipment,  or  $200,000,  leaving 
$934,480  as  the  present  value  of  the  profit  in  sight.  A  further 
refinement  could  be  added  by  calculating  the  interest  charge- 
able against  the  $200,000  equipment  cost  up  to  the  time  of  pro- 
duction. 

TABLE  III. 


Annual 
Rate  of 
Dividend. 

Number  of  years  of  life  required  to  yield  —  %  interest,  and  in  addition  to  furnish 
annual  instalments  which,  if  reinvested  at  4%,  will  return  the  original  investment  at 
the  end  of  the  period. 

% 

5% 

c% 

T% 

8% 

9% 

10% 

6 

41.0 

7 

28.0 

41.0 

8 

21.6 

28.0 

41.0 

9 

17.7 

21.6 

28.0 

41.0 

10 

15.0 

17.7 

21.6 

28.0 

41.0 

11 

13.0 

15.0 

17.7 

21.6 

28.0 

41.0 

12 

11.5 

13.0 

15.0 

17.7 

21.6 

28.0 

13 

10.3 

11.5 

13.0 

15.0 

17.7 

21.6 

14 

9.4 

10.3 

11.5 

13.0 

15.0 

17.7 

15 

8.6 

9.4 

10.3 

11.5 

13.0 

15.0 

16 

7.9 

8.6 

9.4 

10.3 

11.5 

13.0 

17 

7.3 

7.9 

8.6 

9.4 

10.3 

11.5 

18 

6.8 

7.3 

7.9 

8.6 

9.4 

10.3 

19 

6.4 

6.8 

7.3 

7.9 

8.6 

9.4 

20 

6.0 

6.4 

6.8 

7.3 

7.9 

8.6 

21 

5.7 

6.0 

6.4 

6.8 

7.3 

7.9 

22 

5.4 

5.7 

6.0 

6.4 

6.8 

7.3 

23 

5.1 

5.4 

5.7 

6.0 

6.4 

6.8 

24 

4.9 

5.1 

5.4 

5.7 

6.0 

6.4 

25 

4.7 

4.9 

5.1 

5.4 

5.7 

6.0 

26 

4.5 

4.7 

4.9 

5.1 

5.4 

5.7 

27 

4.3 

4.5 

4.7 

4.9 

5.1 

5.4 

28 

4.1 

4.3 

4.5 

4.7 

4.9 

5.1 

29 

3.9 

4.1 

4.3 

4.5 

4.7 

4.9 

30 

3.8 

3.9 

4.1 

4.3 

4.5 

4.7 

MINE  VALUATION.  49 

Table  III.  This  table  is  calculated  by  inversion  of  the  factors 
in  Table  I,  and  is  the  most  useful  of  all  such  tables,  as  it  is  a 
direct  calculation  of  the  number  of  years  that  a  given  rate  of 
income  on  the  investment  must  continue  in  order  to  amortize 
the  capital  (the  annual  sinking  fund  being  placed  at  compound 
interest  at  4%)  and  to  repay  various  rates  of  interest  on  the 
investment.  The  application  of  this  method  in  testing  the  value 
of  dividend-paying  shares  is  very  helpful,  especially  in  weighing 
the  risks  involved  in  the  portion  of  the  purchase  or  investment 
unsecured  by  the  profit  in  sight.  Given  the  annual  percentage 
income  on  the  investment  from  the  dividends  of  the  mine  (or  on 
a  non-producing  mine  assuming  a  given  rate  of  production  and 
profit  from  the  factors  exposed),  by  reference  to  the  table  the 
number  of  years  can  be  seen  in  which  this  percentage  must  con- 
tinue in  order  to  amortize  the  investment  and  pay  various  rates 
of  interest  on  it.  As  said  before,  the  ore  in  sight  at  a  given  rate 
of  exhaustion  can  be  reduced  to  terms  of  life  in  sight.  This 
certain  period  deducted  from  the  total  term  of  years  required 
gives  the  life  which  must  be  provided  by  further  discovery  of 
ore,  and  this  can  be  reduced  to  tons  or  feet  of  extension  of  given 
ore-bodies  and  a  tangible  position  arrived  at.  The  test  can  be 
applied  in  this  manner  to  the  various  prices  which  must  be 
realized  from  the  base  metal  in  sight  to  warrant  the  price. 

Taking  the  last  example  and  assuming  that  the  mine  is 
equipped,  and  that  the  price  is  $2,000,000,  the  yearly  return 
on  the  price  is  10%.  If  it  is  desired  besides  amortizing  or  re- 
deeming the  capital  to  secure  a  return  of  7%  on  the  investment, 
it  will  be  seen  by  reference  to  the  table  that  there  will  be  required 
a  life  of  21.6  years.  As  the  life  visible  in  the  ore  in  sight  is  ten 
years,  then  the  extensions  in  depth  must  produce  ore  for  11.6 
years  longer  —  1,160,000  tons.  If  the  ore-body  is  1,000  feet  long 
and  13  feet  wide,  it  will  furnish  of  gold  ore  1,000  tons  per  foot 
of  depth;  hence  the  ore-body  must  extend  1,160  feet  deeper  to 
justify  the  price.  Mines  are  seldom  so  simple  a  proposition  as 
this  example.  There  are  usually  probabilities  of  other  ore;  and 
in  the  case  of  base  metal,  then  variability  of  price  and  other  ele- 
ments must  be  counted.  However,  once  the  extension  in  depth 


50  PRINCIPLES  OF  MINING. 

which  is  necessary  is  determined  for  various  assumptions  of 
metal  value,  there  is  something  tangible  to  consider  and  to  weigh 
with  the  five  geological  weights  set  out  in  Chapter  III. 

The  example  given  can  be  expanded  to  indicate  not  only  the 
importance  of  interest  and  redemption  in  the  long  extension  in 
depth  required,  but  a  matter  discussed  from  another  point  of 
view  under  "Ratio  of  Output."  If  the  plant  on  this  mine  were 
doubled  and  the  earnings  increased  to  20%  ($400,000  per  annum) 
(disregarding  the  reduction  in  working  expenses  that  must  fol- 
low expansion  of  equipment),  it  will  be  found  that  the  life  re- 
quired to  repay  the  purchase  money,  —  $2,000,000,  —  and  7% 
interest  upon  it,  is  about  6.8  years. 

As  at  this  increased  rate  of  production  there  is  in  the  ore  in 
sight  a  life  of  five  years,  the  extension  in  depth  must  be  depended 
upon  for  1.8  years,  or  only  360,000  tons,  — that  is,  360  feet  of  ex- 
tension. Similarly,  the  present  value  of  the  ore  in  sight  is 
$268,000  greater  if  the  mine  be  given  double  the  equipment,  for 
thus  the  idle  money  locked  in  the  ore  is  brought  into  the  interest 
market  at  an  earlier  date.  Against  this  increased  profit  must 
be  weighed  the  increased  cost  of  equipment.  The  value  of 
low  grade  mines,  especially,  is  very  much  a  factor  of  the  volume 
of  output  contemplated. 


CHAPTER  VI. 
MINE  VALUATION  (Concluded). 

VALUATION  OF  MINES  WITH  LITTLE  OR  NO  ORE  IN  SIGHT;  VALUA- 
TIONS ON  SECOND-HAND  DATA ;  GENERAL  CONDUCT  OF  EXAMI- 
NATIONS; REPORTS. 

A  LARGE  number  of  examinations  arise  upon  prospecting  ven- 
tures or  partially  developed  mines  where  the  value  is  almost 
wholly  prospective.  The  risks  in  such  enterprises  amount  to 
the  possible  loss  of  the  whole  investment,  and  the  possible  returns 
must  consequently  be  commensurate.  Such  business  is  therefore 
necessarily  highly  speculative,  but  not  unjustifiable,  as  the  whole 
history  of  the  industry  attests ;  but  this  makes  the  matter  no 
easier  for  the  mine  valuer.  Many  devices  of  financial  procedure 
assist  in  the  limitation  of  the  sum  risked,  and  offer  a  middle  course 
to  the  investor  between  purchase  of  a  wholly  prospective  value 
and  the  loss  of  a  possible  opportunity  to  profit  by  it.  The  usual 
form  is  an  option  to  buy  the  property  after  a  period  which  per- 
mits a  certain  amount  of  development  work  by  the  purchaser 
before  final  decision  as  to  purchase. 

Aside  from  young  mines  such  enterprises  often  arise  from  the 
possibility  of  lateral  extension  of  the  ore-deposit  outside  the 
boundaries  of  the  property  of  original  discovery  (Fig.  3),  in 
which  cases  there  is  often  no  visible  ore  within  the  property 
under  consideration  upon  which  to  found  opinion.  In  regions 
where  vertical  side  lines  obtain,  there  is  always  the  possibility  of 
a  "deep  level"  in  inclined  deposits.  Therefore  the  ground  sur- 
rounding known  deposits  has  a  certain  speculative  value,  upon 
which  engineers  are  often  called  to  pass  judgment.  Except  in 
such  unusual  occurrences  as  South  African  bankets,  or  Lake 
Superior  coppers,  prospecting  for  deep  level  of  extension  is  also 
a  highly  speculative  phase  of  mining. 

51 


52  PRINCIPLES  OF  MINING. 

The  whole  basis  of  opinion  in  both  classes  of  ventures  must 
be  the  few  geological  weights,  —  the  geology  of  the  property  and 
the  district,  the  development  of  surrounding  mines,  etc.  In  any 
event,  there  is  a  very  great  percentage  of  risk,  and  the  profit  to 
be  gained  by  success  must  be,  proportionally  to  the  expenditure 
involved,  very  large.  It  is  no  case  for  calculating  amortization 
and  other  refinements.  It  is  one  where  several  hundreds  or 
thousands  of  per  cent  hoped  for  on  the  investment  is  the  only 
justification. 


OPINIONS  AND  VALUATIONS   UPON  SECOND-HAND   DATA. 

Some  one  may  come  forward  and  deprecate  the  bare  sugges- 
tion of  an  engineer's  offering  an  opinion  when  he  cannot  have 
proper  first-hand  data.  But  in  these  days  we  have  to  deal  with 
conditions  as  well  as  theories  of  professional  ethics.  The  grow- 
ing ownership  of  mines  by  companies,  that  is  by  corporations 
composed  of  many  individuals,  and  with  their  stocks  often  dealt 
in  on  the  public  exchanges,  has  resulted  in  holders  whose  interest 
is  not  large  enough  to  warrant  their  undertaking  the  cost  of 
exhaustive  examinations.  The  system  has  produced  an  in- 
creasing class  of  mining  speculators  and  investors  who  are  find- 
ing and  supplying  the  enormous  sums  required  to  work  our 
mines,  —  sums  beyond  the  reach  of  the  old-class  single-handed 
mining  men.  Every  year  the  mining  investors  of  the  new  order 
are  coming  more  and  more  to  the  engineer  for  advice,  and  they 
should  be  encouraged,  because  such  counsel  can  be  given  within 
limits,  and  these  limits  tend  to  place  the  industry  upon  a  sounder 
footing  of  ownership.  As  was  said  before,  the  lamb  can  be  in  a 
measure  protected.  The  engineer's  interest  is  to  protect  him, 
so  that  the  industry  which  concerns  his  own  life-work  may  be  in 
honorable  repute,  and  that  capital  may  be  readily  forthcoming 
for  its  expansion.  Moreover,  by  constant  advice  to  the  in- 
vestor as  to  what  constitutes  a  properly  presented  and  man- 
aged project,  the  arrangement  of  such  proper  presentation  and 
management  will  tend  to  become  an  a  priori  function  of  the 
promoter. 


MINE  VALUATION.  53 

Sometimes  the  engineer  can  make  a  short  visit  to  the  mine 
for  data  purposes,  —  more  often  he  cannot.  In  the  former  case, 
he  can  resolve  for  himself  an  approximation  upon  all  the  factors 
bearing  on  value,  except  the  quality  of  the  ore.  For  this,  aside 
from  inspection  of  the  ore  itself,  a  look  at  the  plans  is  usually 
enlightening.  A  longitudinal  section  of  the  mine  showing  a  con- 
tinuous shortening  of  the  stopes  with  each  succeeding  level 
carries  its  own  interpretation.  In  the  main,  the  current  record 
of  past  production  and  estimates  of  the  management  as  to  ore- 
reserves,  etc.,  can  be  accepted  in  ratio  to  the  confidence  that  can 
be  placed  in  the  men  who  present  them.  It  then  becomes  a  case 
of  judgment  of  men  and  things,  and  here  no  rule  applies. 

Advice  must  often  be  given  upon  data  alone,  without  in- 
spection of  the  mine.  Most  mining  data  present  internal  evi- 
dence as  to  credibility.  The  untrustworthy  and  inexperienced 
betray  themselves  in  their  every  written  production.  Assuming 
the  reliability  of  data,  the  methods  already  discussed  for 
weighing  the  ultimate  value  of  the  property  can  be  applied. 
It  would  be  possible  to  cite  hundreds  of  examples  of  valuation 
based  upon  second-hand  data.  Three  will,  however,  sufficiently 
illustrate.  First,  the  R  mine  at  Johannesburg.  With  the  regu- 
larity of  this  deposit,  the  development  done,  and  a  study  of  the 
workings  on  the  neighboring  mines  and  in  deeper  ground,  it  is  a 
not  unfair  assumption  that  the  reefs  will  maintain  size  and  value 
throughout  the  area.  The  management  is  sound,  and  all  the 
data  are  given  in  the  best  manner.  The  life  of  the  mine  is 
estimated  at  six  years,  with  some  probabilities  of  further  ore 
from  low-grade  sections.  The  annual  earnings  available  for 
dividends  are  at  the  rate  of  about  £450,000  per  annum. 
The  capital  is  £440,000  in  £1  shares.  By  reference  to  the 
table  on  page  46  it  will  be  seen  that  the  present  value  of 
£450,000  spread  over  six  years  to  return  capital  at  the  end  of 
that  period,  and  give  7%  dividends  in  the  meantime,  is 
4.53  x  £450,000  =  £2,036,500  -*-  440,000  =  £4  12s.  Id.  per 
share.  So  that  this  mine,  on  the  assumption  of  continuity  of 
values,  will  pay  about  7%  and  return  the  price.  Seven  per  cent 
is;  however,  not  deemed  an  adequate  return  for  the  risks  of  labor 


54  PRINCIPLES  OF  MINING 

troubles,  faults,  dykes,  or  poor  patches.  On  a  9%  basis,  the  mine 
is  worth  about  £4  4s.  per  share. 

Second,  the  G  mine  in  Nevada.  It  has  a  capital  of  $10,000,000 
in  $1  shares,  standing  in  the  market  at  50  cents  each.  The  re- 
serves are  250,000  tons,  yielding  a  profit  for  yearly  division  of  $7 
per  ton.  It  has  an  annual  capacity  of  about  100,000  tons,  or 
$700,000  net  profit,  equal  to  14%  on  the  market  value.  In 
order  to  repay  the  capital  value  of  $5,000,000  arid  8%  per  an- 
num, it  will  need  a  life  of  (Table  III)  13  years,  of  which  2J  are 
visible.  The  size  of  the  ore-bodies  indicates  a  yield  of  about 
1,100  tons  per  foot  of  depth.  At  an  exhaustion  rate  of  100,000 
tons  per  annum,  the  mine  would  need  to  extend  to  a  depth  of 
over  a  thousand  feet  below  the  present  bottom.  There  is  always 
a  possibility  of  finding  parallel  bodies  or  larger  volumes  in  depth, 
but  it  would  be  a  sanguine  engineer  indeed  who  would  recom- 
mend the  stock,  even  though  it  pays  an  apparent  14%. 

Third,  the  B  mine,  with  a  capital  of  $10,000,000  in  2,000,000 
shares  of  $5  each.  The  promoters  state  that  the  mine  is  in  the 
slopes  of  the  Andes  in  Peru;  that  there  are  6,000,000  tons  of 
"ore  blocked  out";  that  two  assays  by  the  assay ers  of  the  Bank 
of  England  average  9%  copper;  that  the  copper  can  be  produced 
at  five  cents  per  pound;  that  there  is  thus  a  profit  of  $10,000,000 
in  sight.  The  evidences  are  wholly  incompetent.  It  is  a  gamble 
on  statements  of  persons  who  have  not  the  remotest  idea  of  sound 
mining. 

GENERAL  CONDUCT  OF  EXAMINATION. 

Complete  and  exhaustive  examination,  entailing  extensive 
sampling,  assaying,  and  metallurgical  tests,  is  very  expensive 
and  requires  time.  An  unfavorable  report  usually  means  to  the 
employer  absolute  loss  of  the  engineer's  fee  and  expenses.  It 
becomes  then  the  initial  duty  of  the  latter  to  determine  at  once, 
by  the  general  conditions  surrounding  the  property,  how  far 
the  expenditure  for  exhaustive  examination  is  warranted.  There 
is  usually  named  a  money  valuation  for  the  property,  and  thus 
a  peg  is  afforded  upon  which  to  hang  conclusions.  Very  often 
collateral  factors,  with  a  preliminary  sampling,  or  indeed  no 


MINE  VALUATION.  55 

sampling  at  all,  will  determine  the  whole  business.  In  fact,  it 
is  becoming  very  common  to  send  younger  engineers  to  report 
as  to  whether  exhaustive  examination  by  more  expensive  men  is 
justified. 

In  the  course  of  such  preliminary  inspection,  the  ore-bodies 
may  prove  to  be  too  small  to  insure  adequate  yield  on  the  price, 
even  assuming  continuity  in  depth  and  represented  value.  They 
may  be  so  difficult  to  mine  as  to  make  costs  prohibitive,  or  they 
may  show  strong  signs  of  "petering  out."  The  ore  may  present 
visible  metallurgical  difficulties  which  make  it  unprofitable  in 
any  event.  A  gold  ore  may  contain  copper  or  arsenic,  so  as  to 
debar  cyanidation,  where  this  process  is  the  only  hope  of  suffi- 
ciently moderate  costs.  A  lead  ore  may  be  an  amorphous 
compound  with  zinc,  and  successful  concentration  or  smelting 
without  great  penalties  may  be  precluded.  A  copper  ore  may 
carry  a  great  excess  of  silica  and  be  at  the  same  time  unconcen- 
tratable,  and  there  may  be  no  base  mineral  supply  available  for 
smelting  mixture.  The  mine  may  be  so  small  or  so  isolated 
that  the  cost  of  equipment  will  never  be  justified.  Some  of 
these  conditions  may  be  determined  as  unsurmountable,  assum- 
ing a  given  value  for  the  ore,  and  may  warrant  the  rejection  of 
the  mine  at  the  price  set. 

It  is  a  disagreeable  thing  to  have  a  disappointed  promoter 
heap  vituperation  on  an  engineer's  head  because  he  did  not 
make  an  exhaustive  examination.  Although  it  is  generally 
desirable  to  do  some  sampling  to  give  assurance  to  both  pur- 
chaser and  vendor  of  conscientiousness,  a  little  courage  of  con- 
viction, when  this  is  rightly  and  adequately  grounded,  usually 
brings  its  own  reward. 

Supposing,  however,  that  conditions  are  right  and  that  the 
mine  is  worth  the  price,  subject  to  confirmation  of  values,  the 
determination  of  these  cannot  be  undertaken  unless  time  and 
money  are  available  for  the  work.  As  was  said,  a  sampling 
campaign  is  expensive,  and  takes  time,  and  no  engineer  has  the 
moral  right  to  undertake  an  examination  unless  both  facilities 
are  afforded.  Curtailment  is  unjust,  .both  to  himself  and  to  his 
employer. 


56  PRINCIPLES  OF  MINING. 

How  much  time  and  outlay  are  required  to  properly  sample 
a  mine  is  obviously  a  question  of  its  size,  and  the  character  of  its 
ore.  An  engineer  and  one  principal  assistant  can  conduct  two 
sampling  parties.  In  hard  rock  it  may  be  impossible  to  take 
more  than  five  samples  a  day  for  each  party.  But,  in  average 
ore,  ten  samples  for  each  is  reasonable  work.  As  the  number  of 
samples  is  dependent  upon  the  footage  of  openings  on  the  de- 
posit, a  rough  approximation  can  be  made  in  advance,  and  a 
general  idea  obtained  as  to  the  time  required.  This  period  must 
be  insisted  upon. 

REPORTS. 

Reports  are  to  be  read  by  the  layman,  and  their  first  quali- 
ties should  be  simplicity  of  terms  and  definiteness  of  conclu- 
sions. Reports  are  usually  too  long,  rather  than  too  short. 
The  essential  facts  governing  the  value  of  a  mine  can  be  expressed 
on  one  sheet  of  paper.  It  is  always  desirable,  however,  that  the 
groundwork  data  and  the  manner  of  their  determination  should 
be  set  out  with  such  detail  that  any  other  engineer  could  come 
to  the  same  conclusion  if  he  accepted  the  facts  as  accurately 
determined.  In  regard  to  the  detailed  form  of  reports,  the 
writer's  own  preference  is  for  a  single  page  summarizing  the 
main  factors,  and  an  assay  plan,  reduced  to  a  longitudinal  sec- 
tion where  possible.  Then  there  should  be  added,  for  purposes 
of  record  and  for  submission  to  other  engineers,  a  set  of  appen- 
dices going  into  some  details  as  to  the  history  of  the  mine,  its 
geology,  development,  equipment,  metallurgy,  and  management. 
A  list  of  samples  should  be  given  with  their  location,  and  the 
tonnages  and  values  of  each  separate  block.  A  presentation 
should  be  made  of  the  probabilities  of  extension  in  depth,  to- 
gether with  recommendations  for  working  the  mine. 

GENERAL   SUMMARY. 

The  bed-rock  value  which  attaches  to  a  mine  is  the  profit 
to  be  won  from  proved  ore  and  in  which  the  price  of  metal  is 
calculated  at  some  figure  between  "basic"  and  "normal." 
This  we  may  call  the  "A  "  value.  Beyond  this  there  is  the  spec- 


MINE  VALUATION.  57 

ulative  value  of  the  mine.  If  the  value  of  the  "probable"  ore 
be  represented  by  X,  the  value  of  extension  of  the  ore  by  Y,  and 
a  higher  price  for  metal  than  the  price  above  assumed  represented 
by  Z,  then  if  the  mine  be  efficiently  managed  the  value  of  the 
mine  is  A  +  X  +  Y  +  Z.  What  actual  amounts  should  be 
attached  to  X,  Y,  Z  is  a  matter  of  judgment.  There  is  no 
prescription  for  good  judgment.  Good  judgment  rests  upon  a 
proper  balancing  of  evidence.  The  amount  of  risk  in  X,  Y,  Z 
is  purely  a  question  of  how  much  these  factors  are  required  to 
represent  in  money,  —  in  effect,  how  much  more  ore  must  be 
found,  or  how  many  feet  the  ore  must  extend  in  depth;  or  in 
convertible  terms,  what  life  in  years  the  mine  must  have,  or  how 
high  the  price  of  metal  must  be.  In  forming  an  opinion  whether 
these  requirements  will  be  realized,  X,  Y,  Z  must  be  balanced  in 
a  scale  whose  measuring  standards  are  the  five  geological  weights 
and  the  general  industrial  outlook.  The  wise  engineer  will  put 
before  his  clients  the  scale,  the  weights,  and  the  conclusion 
arrived  at.  The  shrewd  investor  will  require  to  know  these  of 
his  adviser. 


CHAPTER  VII. 
DEVELOPMENT  OF  MINES. 

ENTRY  TO  THE  MINE;  TUNNELS;  VERTICAL,  INCLINED,  AND  COM- 
BINED SHAFTS;  LOCATION  AND  NUMBER  OF  SHAFTS. 

DEVELOPMENT  is  conducted  for  two  purposes:  first,  to  search 
for  ore ;  and  second,  to  open  avenues  for  its  extraction.  Although 
both  objects  are  always  more  or  less  in  view,  the  first  predomi- 
nates in  the  early  life  of  mines,  the  prospecting  stage,  and  the 
second  in  its  later  life,  the  producing  stage.  It  is  proposed 
to  discuss  development  designed  to  embrace  extended  produc- 
tion purposes  first,  because  development  during  the  prospecting 
stage  is  governed  by  the  same  principles,  but  is  tempered  by  the 
greater  degree  of  uncertainty  as  to  the  future  of  the  mine,  and 
is,  therefore,  of  a  more  temporary  character. 

ENTRY  TO   THE   MINE. 

There  are  four  methods  of  entry:  by  tunnel,  vertical  shaft, 
inclined  shaft,  or  by  a  combination  of  the  last  two,  that  is,  by  a 
shaft  initially  vertical  then  turned  to  an  incline.  Combined 
shafts  are  largely  a  development  of  the  past  few  years  to  meet 
"deep  level"  conditions,  and  have  been  rendered  possible  only 
by  skip-winding.  The  angle  in  such  shafts  (Fig.  2)  is  now  gen- 
erally made  on  a  parabolic  curve,  and  the  speed  of  winding  is 
then  less  diminished  by  the  bend. 

The  engineering  problems  which  present  themselves  under 
"entry"  may  be  divided  into  those  of:  — 

1.  Method. 

2.  Location. 

3.  Shape  and  size. 

58 


DEVELOPMENT  OF  MINES. 


59 


The  resolution  of  these  questions  depends  upon  the :  — 

a.  Degree  of  dip  of  the  deposit. 

b.  Output  of  ore  to  be  provided  for. 

c.  Depth  at  which  the  deposit  is  to  be  attacked. 

d.  Boundaries  of  the  property. 
Surface  topography. 

/.    Cost. 

g.    Operating  efficiency. 

h.   Prospects  of  the  mine. 


e. 


FIG.  2.  —  Showing  arrangement  of  the  bend  in  combined  shafts. 


60  PRINCIPLES  OF  MINING. 

From  the  point  of  view  of  entrance,  the  cooperation  of  a 
majority  of  these  factors  permits  the  division  of  mines  into  cer- 
tain broad  classes.  The  type  of  works  demanded  for  moderate 
depths  (say  vertically  2,500  to  3,000  feet)  is  very  different  from 
that  required  for  great  depths.  To  reach  great  depths,  the  size 
of  shafts  must  greatly  expand,  to  provide  for  extended  ventila- 
tion, pumping,  and  winding  necessities.  Moreover  inclined 
shafts  of  a  degree  of  flatness  possible  for  moderate  depths  be- 
come too  long  to  be  used  economically  from  the  surface.  The 
vast  majority  of  metal-mining  shafts  fall  into  the  first  class, 
those  of  moderate  depths.  Yet,  as  time  goes  on  and  ore-de- 
posits are  exhausted  to  lower  planes,  problems  of  depth  will 
become  more  common.  One  thing,  however,  cannot  be  too 
much  emphasized,  especially  on  mines  to  be  worked  from  the 
outcrop,  and  that  is,  that  no  engineer  is  warranted,  owing  to 
the  speculation  incidental  to  extension  in  depth,  in  initiating 
early  in  the  mine's  career  shafts  of  such  size  or  equipment  as 
would  be  available  for  great  depths.  Moreover,  the  proper  loca- 
tion -  of  a  shaft  so  as  to  work  economically  extension  of  the 
ore-bodies  is  a  matter  of  no  certainty,  and  therefore  shafts  of 
speculative  mines  are  tentative  in  any  event. 

Another  line  of  division  from  an  engineering  view  is  brought 
about  by  a  combination  of  three  of  the  factors  mentioned.  This 
is  the  classification  into  " outcrop"  and  " deep-level"  mines. 
The  former  are  those  founded  upon  ore-deposits  to  be  worked 
from  or  close  to  the  surface.  The  latter  are  mines  based  upon 
the  extension  in  depth  of  ore-bodies  from  outcrop  mines.  Such 
projects  are  not  so  common  in  America,  where  the  law  in  most 
districts  gives  the  outcrop  owner  the  right  to  follow  ore  beyond 
his  side-lines,  as  in  countries  where  the  boundaries  are  vertical 
on  all  sides.  They  do,  however,  arise  not  alone  in  the  few 
American  sections  where  the  side-lines  are  vertical  boundaries, 
but  in  other  parts  owing  to  the  pitch  of  ore-bodies  through  the 
end  lines  (Fig.  3).  More  especially  do  such  problems  arise  in 
America  in  effect,  where  the  ingress  questions  have  to  be  re- 
vised for  mines  worked  out  in  the  upper  levels  (Fig.  7) . 

If  from  a  standpoint  of  entrance  questions,  mines  are  first 


61 


62    '  PRINCIPLES   OF  MINING. 

classified  into  those  whose  works  are  contemplated  for  moderate 
depths,  and  those  in  which  work  is  contemplated  for  great 
depth,  further  clarity  in  discussion  can  be  gained  by  subdivision 
into  the  possible  cases  arising  out  of  the  factors  of  location,  dip, 
topography,  and  boundaries. 

MINES  OF  MODERATE  DEPTHS. 

Case  I.  Deposits   where   topographic    conditions   permit   the 

alternatives  of  shaft  or  tunnel. 

Case  II.  Vertical   or  horizontal   deposits,   the   only   practical 
means  of  attaining  which  is  by  a  vertical  shaft. 

Case  III.  Inclined  deposits  to  be  worked  from  near  the  surface. 
There  are  in  such  instances  the  alternatives  of  either 
a  vertical  or  an  inclined  shaft. 

Case  IV.  Inclined  deposits  which  must  be  attacked  in  depth, 
that  is,  deep-level  projects.  There  are  the  alterna- 
tives of  a  compound  shaft  or  of  a  vertical  shaft,  and 
in  some  cases  of  an  incline  from  the  surface. 


MINES   TO    GREAT    DEPTHS. 

Case  V.  Vertical  or  horizontal  deposits,  the  only  way  of  reach- 
ing which  is  by  a  vertical  shaft. 

Case  VI.  Inclined  deposits.     In  such  cases  the  alternatives  are 
a  vertical  or  a  compound  shaft. 

Case  I.  —  Although  for  logical  arrangement  tunnel  entry 
has  been  given  first  place,  to  save  repetition  it  is  proposed  to 
consider  it  later.  With  few  exceptions,  tunnels  are  a  temporary 
expedient  in  the  mine,  which  must  sooner  or  later  be  opened  by 
a  shaft. 

Case  II.  Vertical  or  Horizontal  Deposits.  —  These  require  no 
discussion  as  to  manner  of  entry.  There  is  no  justifiable  alterna- 
tive to  a  vertical  shaft  (Fig.  4). 

Case  III.  Inclined  Deposits  which  are  intended  to  be  worked 
from  the  Outcrop,  or  from  near  It  (Fig.  5).  —  The  choice  of 
inclined  or  vertical  shaft  is  dependent  upon  relative  cost  of  con- 


Levet 


FIG.  4.  —  Cross-sections  showing  entry  to  vertical  or  horizontal  deposits.     Case  II. 


/TjP^V  A 


FIG.  5.  —  Cross-section  showing  alternative  shafts  to  inclined  deposit  to  be  worked 
from  surface.     Case  III. 


64  PRINCIPLES  OF  MINING. 

struction,  subsequent  operation,  and  the  useful  life  of  the  shaft, 
and  these  matters  are  largely  governed  by  the  degree  of  dip. 
Assuming  a  shaft  of  the  same  size  in  either  alternative,  the  com- 
parative cost  per  foot  of  sinking  is  dependent  largely  on  the 
breaking  facilities  of  the  rock  under  the  different  directions  of 
attack.  In  this,  the  angles  of  the  bedding  or  joint  planes  to  the 
direction  of  the  shaft  outweigh  other  factors.  The  shaft  which 
takes  the  greatest  advantage  of  such  lines  of  breaking  weakness 
will  be  the  cheapest  per  foot  to  sink.  In  South  African  experi- 
ence, where  inclined  shafts  are  sunk  parallel  to  the  bedding 
planes  of  hard  quartzites,  the  cost  per  foot  appears  to  be  in 
favor  of  the  incline.  On  the  other  hand,  sinking  shafts  across 
tight  schists  seems  to  be  more  advantageous  than  parallel  to  the 
bedding  planes,  and  inclines  following  the  dip  cost  more  per 
foot  than  vertical  shafts. 

An  inclined  shaft  requires  more  footage  to  reach  a  given  point 
of  depth,  and  therefore  it  would  entail  a  greater  total  expense 
than  a  vertical  shaft,  assuming  they  cost  the  same  per  foot. 
The  excess  amount  will  be  represented  by  the  extra  length,  and 
this  will  depend  upon  the  flatness  of  the  dip.  With  vertical 
shafts,  however,  crosscuts  to  the  deposit  are  necessary.  In  a 
comparative  view,  therefore,  the  cost  of  the  crosscuts  must  be 
included  with  that  of  the  vertical  shaft,  as  they  would  be  almost 
wholly  saved  in  an  incline  following  near  the  ore. 

The  factor  of  useful  life  for  the  shaft  enters  in  deciding  as 
to  the  advisability  of  vertical  shafts  on  inclined  deposits,  from 
the  fact  that  at  some  depth  one  of  two  alternatives  has  to  be 
chosen.  The  vertical  shaft,  when  it  reaches  a  point  below  the 
deposit  where  the  crosscuts  are  too  long  ((7,  Fig.  5),  either  be- 
comes useless,  or  must  be  turned  on  an  incline  at  the  inter- 
section with  the  ore  (B).  The  first  alternative  means  ulti- 
mately a  complete  loss  of  the  shaft  for  working  purposes.  The 
latter  has  the  disadvantage  that  the  bend  interferes  slightly  with 
haulage, 

The  following  table  will  indicate  an  hypothetical  extreme 
case,  —  not  infrequently  met.  In  it  a  vertical  shaft  1,500  feet  in 
depth  is  taken  as  cutting  the  deposit  at  the  depth  of  750  feet, 


DEVELOPMENT  OF  MINES. 


65 


the  most  favored  position  so  far  as  aggregate  length  of  crosscuts 
is  concerned.  The  cost  of  crosscutting  is  taken  at  $20  per  foot 
and  that  of  sinking  the  vertical  shaft  at  $75  per  foot.  The  in- 
cline is  assumed  for  two  cases  at  $75  and  $100  per  foot  respec- 
tively. The  stoping  height  upon  the  ore  between  levels  is 
counted  at  125  feet. 


DIP  OF  DEPOSIT 

DEPTH  OF 

LENGTH  OF 

No.  OF  CROSSCUTS 

TOTAL  LENGTH  OF 

FROM  HORIZONTAL 

VERTICAL  SHAFT 

INCLINE  REQUIRED 

REQUIRED  FROM 

CROSSCUTS,  FEET 

V  SHAFT 

80° 

1,500 

1,522 

11 

859 

70° 

1,500 

1,595 

12 

1,911 

60° 

1,500 

1,732 

13 

3,247 

50° 

1,500 

1,958 

15 

5,389 

40° 

1,500 

2,334 

18 

8,938 

30° 

1,500 

3,000 

23 

16,237 

COST  OF  CROSSCUTS 
$20  PER  FOOT 

COST  VERTICAL 
SHAFT  $75  PER 
FOOT 

TOTAL  COST  OF 
VERTICAL  AND 
CROSSCUTS 

COST  OF  INCLINE 
$75  PER  FOOT 

COST  OF  INCLINE 
$100  PER  FOOT 

$17,180 

$112,500 

$129,680 

$114,150 

$152,200 

38,220 

112,500 

150,720 

118,025 

159,500 

64,940 

112,500 

177,440 

129,900 

172,230 

107,780 

112,500 

220,280 

114,850 

195,800 

178,760 

112,500 

291,260 

175,050 

233,400 

324,740 

112,500 

437,240 

225,000 

300,000 

From  the  above  examples  it  will  be  seen  that  the  cost  of  cross^ 
cuts  put  at  ordinary  level  intervals  rapidly  outruns  the  extra 
expense  of  increased  length  of  inclines.  If,  however,  the  con- 
ditions are  such  that  crosscuts  from  a  vertical  shaft  are  not 
necessary  at  so  frequent  intervals,  then  in  proportion  to  the 
decrease  the  advantages  sway  to  the  vertical  shaft.  Most  situa- 
tions wherein  the  crosscuts  can  be  avoided  arise  in  mines  worked 
out  in  the  upper  levels  and  fall  under  Case  IV,  that  of  deep- 
level  projects. 

There  can  be  no  doubt  that  vertical  shafts  are  cheaper  to 
operate  than  inclines :  the  length  of  haul  from  a  given  depth  is 
less;  much  higher  rope  speed  is  possible,  and  thus  the  haulage 
hours  are  less  for  the  same  output;  the  wear  and  tear  on  ropes, 


66 


PRINCIPLES   OF  MINING. 


tracks,  or  guides  is  not  so  great,  and  pumping  is  more  economical 
where  the  Cornish  order  of  pump  is  used.  On  the  other  hand, 
with  a  vertical  shaft  must  be  included  the  cost  of  operating 
crosscuts.  On  mines  where  the  volume  of  ore  does  not  warrant 
mechanical  haulage,  the  cost  of  tramming  through  the  extra  dis- 
tance involved  is  an  expense  which  outweighs  any  extra  operat- 
ing outlay  in  the  inclined  shaft  itself.  Even  with  mechanical 
haulage  in  crosscuts,  it  is  doubtful  if  there  is  anything  in  favor 
of  the  vertical  shaft  on  this  score. 


FIG.  6.  — Cross-section  showing  auxiliary  vertical  outlet. 

In  deposits  of  very  flat  dips,  under  30°,  the  case  arises  where 
the  length  of  incline  is  so  great  that  the  saving  on  haulage 
through  direct  lift  warrants  a  vertical  shaft  as  an  auxiliary  out- 
let in  addition  to  the  incline  (Fig.  6) .  In  such  a  combination 
the  crosscut  question  is  eliminated.  The  mine  is  worked  above 
and  below  the  intersection  by  incline,  and  the  vertical  shaft  be- 
comes simply  a  more  economical  exit  and  an  alternative  to  secure 
increased  output.  The  North  Star  mine  at  Grass  Valley  is  an 
illustration  in  point.  Such  a  positive  instance  borders  again  on 
Case  IV,  deep-level  projects. 

In  conclusion,  it  is  the  writer's  belief  that  where  mines  are 
to  be  worked  from  near  the  surface,  coincidentally  with  sinking, 
and  where,  therefore,  crosscuts  from  a  vertical  shaft  would  need 
to  be  installed  frequently,  inclines  are  warranted  in  all  dips  under 
75°  and  over  30°.  Beyond  75°  the  best  alternative  is  often 


DEVELOPMENT  OF  MINES.  67 

undeterminable.  In  the  range  under  30°  and  over  15°,  although 
inclines  are  primarily  necessary  for  actual  delivery  of  ore  from 
levels,  they  can  often  be  justifiably  supplemented  by  a  vertical 
shaft  as  a  relief  to  a  long  haul.  In  dips  of  less  than  15°,  as  in 
those  over  75°,  the  advantages  again  trend  strongly  in  favor  of 
the  vertical  shaft.  There  arise,  however,  in  mountainous  coun- 
tries, topographic  conditions  such  as  the  dip  of  deposits  into  the 
mountain,  which  preclude  any  alternative  on  an  incline  at  any 
angled  dip. 

Case  IV.  Inclined  Deposits  which  must  be  attacked  in  Depth 
(Fig.  7) .  —  There  are  two  principal  conditions  in  which  such 
properties  exist:  first,  mines  being  operated,  or  having  been 
previously  worked,  whose  method  of  entry  must  be  revised; 
second,  those  whose  ore-bodies  to  be  attacked  do  not  outcrop 
within  the  property. 

The  first  situation  may  occur  in  mines  of  inadequate  shaft 
capacity  or  wrong  location ;  in  mines  abandoned  and  resurrected ; 
in  mines  where  a  vertical  shaft  has  reached  its  limit  of  useful 
extensions,  having  passed  the  place  of  economical  crosscutting; 
or  in  mines  in  flat  deposits  with  inclines  whose  haul  has  become 
too  long  to  be  economical.  Three  alternatives  present  them- 
selves in  such  cases :  a  new  incline  from  the  surface  (A  B  F,  Fig. 
7),  or  a  vertical  shaft  combined  with  incline  extension  (C  D  F), 
or  a  simple  vertical  shaft  (H  G).  A  comparison  can  be  first 
made  between  the  simple  incline  and  the  combined  shaft.  The 
construction  of  an  incline  from  the  surface  to  the  ore-body  will  be 
more  costly  than  a  combined  shaft,  for  until  the  horizon  of  the 
ore  is  reached  (at  D)  no  crosscuts  are  required  in  the  vertical 
section,  while  the  incline  must  be  of  greater  length  to  reach  the 
same  horizon.  The  case  arises,  however,  where  inclines  can  be 
sunk  through  old  stopes,  and  thus  more  cheaply  constructed 
than  vertical  shafts  through  solid  rock;  and  also  the  case  of 
mountainous  topographic  conditions  mentioned  above. 

From  an  operating  point  of  view,  the  bend  in  combined  shafts 
(at  D)  gives  rise  to  a  good  deal  of  wear  and  tear  on  ropes  and  gear. 
The  possible  speed  of  winding  through  a  combined  shaft  is,  however, 
greater  than  a  simple  incline,  for  although  haulage  speed  through 


68 


PRINCIPLES   OF  MINING. 


the  incline  section  (D  F)  and  around  the  bend  of  the  combined 
shaft  is  about  the  same  as  throughout  a  simple  incline  (A  F), 
the  speed  can  be  accelerated  in  the  vertical  portion  (D  C)  above 
that  feasible  did  the  incline  extend  to  the  surface.  There  is 


FIG.  7.  —  Cross-section  of  inclined  deposit,  which  must  be  attacked  in  depth. 

therefore  an  advantage  in  this  regard  in  the  combined  shaft. 
The  net  advantages  of  the  combined  over  the  inclined  shaft 
depend  on  the  comparative  length  of  the  two  alternative  routes 
from  the  intersection  (D)  to  the  surface.  Certainly  it  is  not 
advisable  to  sink  a  combined  shaft  to  cut  a  deposit  at  300  feet  in 
depth  if  a  simple  incline  can  be  had  to  the  surface.  On  the 


DEVELOPMENT  OF  MINES.  69 

other  hand,  a  combined  shaft  cutting  the  deposit  at  1,000  feet  will 
be  more  advisable  than  a  simple  incline  2,000  feet  long  to  reach 
the  same  point.  The  matter  is  one  for  direct  calculation  in  each 
special  case.  In  general,  there  are  few  instances  of  really  deep- 
level  projects  where  a  complete  incline  from  the  surface  is 
warranted. 

In  most  situations  of  this  sort,  and  in  all  of  the  second  type 
(where  the  outcrop  is  outside  the  property),  actual  choice  usually 
lies  between  combined  shafts  (C  D  F)  and  entire  vertical  shafts 
(H  G).  The  difference  between  a  combined  shaft  and  a  direct 
vertical  shaft  can  be  reduced  to  a  comparison  of  the  combined 
shaft  below  the  point  of  intersection  (D)  with  that  portion  of  a 
vertical  shaft  which  would  cover  the  same  horizon.  The  ques- 
tion then  becomes  identical  with  that  of  inclined  versus  verticals, 
as  stated  in  Case  III,  with  the  offsetting  disadvantage  of  the  bend 
in  the  combined  shaft.  If  it  is  desired  to  reach  production  at  the 
earliest  date,  the  lower  section  of  a  simple  vertical  shaft  must 
have  crosscuts  to  reach  the  ore  lying  above  the  horizon  of  its 
intersection  (E) .  If  production  does  not  press,  the  ore  above  the 
intersection  (EB)  can  be  worked  by  rises  from  the  horizon  of 
intersection  (E).  In  the  use  of  rises,  however,  there  follow 
the  difficulties  of  ventilation  and  lowering  the  ore  down  to  the 
shaft,  which  brings  expenses  to  much  the  same  thing  as  operating 
through  crosscuts. 

The  advantages  of  combined  over  simple  vertical  shafts  are 
earlier  production,  saving,  of  either  rises  or  crosscuts,  and  the 
ultimate  utility  of  the  shaft  to  any  depth.  The  disadvantages 
are  the  cost  of  the  extra  length  of  the  inclined  section,  slower 
winding,  and  greater  wear  and  tear  within  the  inclined  section 
and  especially  around  the  bend.  All  these  factors  are  of  variable 
import,  depending  upon  the  dip.  On  very  steep  dips,  —  over 
70°,  —  the  net  result  is  in  favor  of  the  simple  vertical  shaft.  On 
other  dips  it  is  in  favor  of  the  combined  shaft. 

Cases  V  and  VI.  Mines  to  be  worked  to  Great  Depths,  —  over 
3,000  Feet.  —  In  Case  V,  with  vertical  or  horizontal  deposits, 
there  is  obviously  no  desirable  alternative  to  vertical  shafts. 

In  Case  VI,  with  inclined  deposits,  there  are  the  alternatives 


70  PRINCIPLES   OF  MINING. 

of  a  combined  or  of  a  simple  vertical  shaft.  A  vertical  shaft  in 
locations  (H,  Fig.  7)  such  as  would  not  necessitate  extension  in 
depth  by  an  incline,  would,  as  in  Case  IV,  compel  either  crosscuts 
to  the  ore  or  inclines  up  from  the  horizon  of  intersection  (E). 
Apart  from  delay  in  coming  to  production  and  the  consequent 
loss  of  interest  on  capital,  the  ventilation  problems  with  this 
arrangement  would  be  appalling.  Moreover,  the  combined 
shaft,  entering  the  deposit  near  its  shallowest  point,  offers  the 
possibility  of  a  separate  haulage  system  on  the  inclined  and  on  the 
vertical  sections,  and  such  separate  haulage  is  usually  advisable 
at  great  depths.  In  such  instances,  the  output  to  be  handled  is 
large,  for  no  mine  of  small  output  is  likely  to  be  contemplated  at 
such  depth.  Several  moderate-sized  inclines  from  the  horizon 
of  intersection  have  been  suggested  (EF,  DG,  CH,  Fig.  8)  to  feed 
a  large  primary  shaft  (A B),  which  thus  becomes  the  trunk 
road.  This  program  would  cheapen  lateral  haulage  under- 
ground, as  mechanical  traction  can  be  used  in  the  main  level, 
(EC),  and  horizontal  haulage  costs  can  be  reduced  on  the  lower 
levels.  Moreover,  separate  winding 'engines  on  the  two  sections 
increase  the  capacity,  for  the  effect  is  that  of  two  trains  instead 
of  one  running  on  a  single  track. 

Shaft  Location.  —  Although  the  prime  purpose  in  locating  a 
shaft  is  obviously  to  gain  access  to  the  largest  volume  of  ore 
within  the  shortest  haulage  distance,  other  conditions  also 
enter,  such  as  the  character  of  the  surface  and  the  rock  to  be 
intersected,  the  time  involved  before,  reaching  production,  and 
capital  cost.  As  shafts  must  bear  two  relations  to  a  deposit,  - 
one  as  to  the  dip  and  the  other  as  to  the  strike,  —  they  may  be 
considered  from  these  aspects.  Vertical  shafts  must  be  on  the 
hanging- wall  side  of  the  outcrop  if  the  deposit  dips  at  all.  In 
any  event,  the  shaft  should  be  far  enough  away  to  be  out  of  the 
reach  of  creeps.  An  inclined  shaft  may  be  sunk  either  on  the 
vein,  in  which  case  a  pillar  of  ore  must  be  left  to  support  the 
shaft ;  or,  instead,  it  may  be  sunk  a  short  distance  in  the  footwall, 
and  where  necessary  the  excavation  above  can  be  supported 
by  filling.  Following  the  ore  has  the  advantage  of  prospecting  in 
sinking,  and  in  many  cases  the  softness  of  the  ground  in  the  region 


DEVELOPMENT  OF  MINES. 


71 


of  the  vein  warrants  this  procedure.  It  has,  however,  the  dis- 
advantage that  a  pillar  of  ore  is  locked  up  until  the  shaft  is 
ready  for  abandonment.  Moreover,  as  veins  or  lodes  are  seldom 
of  even  dip,  an  inclined  shaft,  to  have  value  as  a  prospecting 


FIG.  8.  —  Longitudinal  section  showing  shaft  arrangement  proposed  for  very  deep 

inclined  deposits. 

opening,  or  to  take  advantage  of  breaking  possibilities  in  the 
lode,  will  usually  be  crooked,  and  an  incline  irregular  in  detail 
adds  greatly  to  the  cost  of  winding  and  maintenance.  These  twin 
disadvantages  usually  warrant  a  straight  incline  in  the  footwall. 
Inclines  are  not  necessarily  of  the  same  dip  throughout,  but  for 


72  PRINCIPLES  OF  MINING. 

reasonably  economical  haulage  change  of  angle  must  take  place 
gradually. 

In  the  case  of  deep-level  projects  on  inclined  deposits,  de- 
manding combined  or  vertical  shafts,  the  first  desideratum  is 
to  locate  the  vertical  section  as  far  from  the.  outcrop  as  possible, 
and  thus  secure  the  most  ore  above  the  horizon  of  intersection. 
This,  however,  as  stated  before,  would  involve  the  cost  of  cross- 
cuts or  rises  and  would  cause  delay  in  production,  together  with  the 
accumulation  of  capital  charges.  How  important  the  increment 
of  interest  on  capital  may  become  during  the  period  of  opening  the 
mine  may  be  demonstrated  by  a  concrete  case.  For  instance,  the 
capital  of  a  company  or  the  cost  of  the  property  is,  say,  SI, 000,000, 
and  where  opening  the  mine  for  production  requires  four  years, 
the  aggregate  sum  of  accumulated  compound  interest  at  5%  (and 
most  operators  want  more  from  a  mining  investment)  would  be 
$216,000.  Under  such  circumstances,  if  a  year  or  two  can  be 
saved  in  getting  to  production  by  entering  the  property  at  a 
higher  horizon,  the  difference  in  accumulated  interest  will  more 
than  repay  the  infinitesimal  extra  cost  of  winding  through  a  com- 
bined shaft  of  somewhat  increased  length  in  the  inclined  section. 

The  unknown  character  of  the  ore  in  depth  is  always  a  sound 
reason  for  reaching  it  as  quickly  and  as  cheaply  as  possible. 
In  result,  such  shafts  are  usually  best  located  when  the  vertical 
section  enters  the  upper  portion  of  the  deposit. 

The  objective  in  location  with  regard  to  the  strike  of  the  ore- 
bodies  is  obviously  to  have  an  equal  length  of  lateral  ore-haul 
in  every  direction  from  the  shaft.  It  is  easier  to  specify  than  to 
achieve  this,  for  in  all  speculative  deposits  ore-shoots  are  found 
to  pursue  curious  vagaries  as  they  go  down.  Ore-bodies  do  not  re- 
occur with  the  same  locus  as  in  the  upper  levels,  and  generally  the 
chances  to  go  wrong  are  more  numerous  than  those  to  go  right. 

Number  of  Shafts.  —  The  problem  of  whether  the  mine  is  to 
be  opened  by  one  or  by  two  shafts  of  course  influences  location. 
In  metal  mines  under  Cases  II  and  III  (outcrop  properties) 
the  ore  output  requirements  are  seldom  beyond  the  capacity 
of  one  shaft.  Ventilation  and  escape- ways  are  usually  easily 
managed  through  the  old  stopes.  Under  such  circumstances,  the 


DEVELOPMENT  OF  MINES.  73 

conditions  warranting  a  second  shaft  are  the  length  of  under- 
ground haul  and  isolation  of  ore-bodies  or  veins.  Lateral  haul- 
age underground  is  necessarily  disintegrated  by  the  various  levels, 
and  usually  has  to  be  done  by  hand.  By  shortening  this  distance 
of  tramming  and  by  consolidation  of  the  material  from  all  levels 
at  the  surface,  where  mechanical  haulage  can  be  installed,  a 
second  shaft  is  often  justified.  There  is  therefore  an  economic 
limitation  to  the  radius  of  a  single  shaft,  regardless  of  the 
ability  of  the  shaft  to  handle  the  total  output. 

Other  questions  also,  often  arise  which  are  of  equal  im- 
portance to  haulage  costs.  Separate  ore-shoots  or  ore-bodies  or 
parallel  deposits  necessitate,  if  worked  from  one  shaft,  constant 
levels  through  unpayable  ground  and  extra  haul  as  well,  or  ore- 
bodies  may  dip  away  from  the  original  shaft  along  the  strike  of  the 
deposit  and  a  long  haulage  through  dead  levels  must  follow.  For 
instance,  levels  and  crosscuts  cost  roughly  one-quarter  as  much  per 
foot  as  shafts.  Therefore  four  levels  in  barren  ground,  to  reach  a 
parallel  vein  or  isolated  ore-body  1,000  feet  away,  would  pay  for  a 
shaft  1,000  feet  deep.  At  a  depth  of  1,000  feet,  at  least  six  levels 
might  be  necessary.  The  tramming  of  ore  by  hand  through  such  a 
distance  would  cost  about  double  the  amount  to  hoist  it  through  a 
shaft  and  transport  it  mechanically  to  the  dressing  plant  at  surface. 
The  aggregate  cost  and  operation  of  barren  levels  therefore  soon 
pays  for  a  second  shaft.  If  two  or  more  shafts  are  in  question, 
they  must  obviously  be  set  so  as  to  best  divide  the  work. 

Under  Cases  IV,  V,  and  VI, — that  is,  deep-level  projects, — 
ventilation  and  escape  become  most  important  considerations. 
Even  where  the  volume  of  ore  is  within  the  capacity  of  a  single 
shaft,  another  usually  becomes  a  necessity  for  these  reasons. 
Their  location  is  affected  not  only  by  the  locus  of  the  ore,  but,  as 
said,  by  the  time  required  to  reach  it.  Where  two  shafts  are  to  be 
sunk  to  inclined  deposits,  it  is  usual  to  set  one  so  as  to  intersect 
the  deposit  at  a  lower  point  than  the  other.  Production  can  be 
started  from  the  shallower,  before  the  second  is  entirely  ready. 
The  ore  above  the  horizon  of  intersection  of  the  deeper  shaft  is  thus 
accessible  from  the  shallower  shaft,  and  the  difficulty  of  long  rises 
or  crosscuts  from  that  deepest  shaft  does  not  arise. 


CHAPTER  VIII. 
DEVELOPMENT  OF  MINES  (Continued}. 

SHAPE    AND    SIZE    OF    SHAFTS;    SPEED    OF    SINKING;   TUNNELS. 

Shape  of  Shafts. —  Shafts  may  be  round  or  rectangular.* 
Round  vertical  shafts  are  largely  applied  to  coal-mines,  and 
some  engineers  have  advocated  their  usefulness  to  the  mining 
of  the  metals  under  discussion.  Their  great  advantages  lie  in 
their  structural  strength,  in  the  large  amount  of  free  space  for  ven- 
tilation, and  in  the  fact  that  if  walled  with  stone,  brick,  concrete, 
or  steel,  they  can  be  made  water-tight  so  as  to  prevent  inflow  from 
water-bearing  strata,  even  when  under  great  pressure.  The  round 
walled  shafts  have  a  longer  life  than  timbered  shafts.  All  these 
advantages  pertain  much  more  to  mining  coal  or  iron  than 
metals,  for  unsound,  wet  ground  .is  often  the  accompaniment  of 
coal-measures,  and  seldom  troubles  metal-mines.  Ventilation 
requirements  are  also  much  greater  in  coal-mines.  From  a 
metal-miner's  standpoint,  round  shafts  are  comparatively  much 
more  expensive  than  the  rectangular  timbered  type.f  For  a 
larger  area  must  be  excavated  for  the  same  useful  space,  and  if 
support  is  needed,  satisfactory  walling,  which  of  necessity  must 
be  brick,  stone,  concrete^  or  steel,  cannot  be  cheaply  accomplished 
under  the  conditions  prevailing  in  most  metal  regions.  Although 
such  shafts  would  have  a  longer  life,  the  duration  of  timbered 
shafts  is  sufficient  for  most  metal  mines.  It  follows  that,  as  timber 
is  the  cheapest  and  all  things  considered  the  most  advantageous 
means  of  shaft  support  for  the  comparatively  temporary  character 
of  metal  mines,  to  get  the  strains  applied  to  the  timbers  in  the 

*  Octagonal  shafts  were  sunk  in  Mexico  in  former  times.  At  each  face 
of  the  octagon  was  a  whim  run  by  mules,  and  hauling  leather  buckets. 

t  The  economic  situation  is  rapidly  arising  in  a  number  of  localities 
that  steel  beams  can  be  usefully  used  instead  of  timber.  The  same  argu- 
ments apply  to  this  type  of  support  that  apply  to  timber. 

74 


DEVELOPMENT  OF  MIKES.  75 

best  manner,  and  to  use  the  minimum  amount  of  it  consistent 
with  security,  and  to  lose  the  least  working  space,  the  shaft 
must  be  constructed  on  rectangular  lines. 

The  variations  in  timbered  shaft  design  arise  from  the  pos- 
sible arrangement  of  compartments.  Many  combinations  can  be 
imagined,  of  which  Figures  9, 10,  11,  12,  13,  and  14  are  examples. 

rrn     nm 

FIG.  9.  FIG.  10. 


"HI 


FIG. II.  ^___ 

""FIG. 12. 


' 


FIG.  13.  FIG.  14 


The  arrangement  of  compartments  shown  in  Figures  9, 10, 11, 
and  13  gives  the  greatest  strength.  It  permits  timbering  to  the 
best  advantage,  and  avoids  the  danger  underground  involved  in 
crossing  one  compartment  to  reach  another.  It  is  therefore 
generally  adopted.  Any  other  arrangement  would  obviously  be 
impossible  in  inclined  or  combined  shafts. 


76  PRINCIPLES  OF  MINING. 

Size  of  Shafts.  —  In  considering  the  size  of  shafts  to  be  in- 
stalled, many  factors  are  involved.  They  are  in  the  main:  — 

a.  Amount  of  ore  to  be  handled. 
6.  Winding  plant. 

c.  Vehicle  of  transport. 

d.  Depth. 

e.  Number  of  men  to  be  worked  underground. 
/.  Amount  of  water. 

g.  Ventilation. 

h.  Character  of  the  ground. 

i.  Capital  outlay. 

j.  Operating  expense. 

It  is  not  to  be  assumed  that  these  factors  have  been  stated  in 
the  order  of  relative  importance.  More  or  less  emphasis  will  be 
attached  to  particular  factors  by  different  engineers,  and  under 
different  circumstances.  It  is  not  possible  to  suggest  any  arbi- 
trary standard  for  calculating  their  relative  weight,  and  they 
are  so  interdependent  as  to  preclude  separate  discussion.  •  The 
usual  result  is  a  compromise  between  the  demands  of  all. 

Certain  factors,  however,  dictate  a  minimum  position,  which 
may  be  considered  as  a  datum  from  which  to  start  consideration. 

Fir st}  a  winding  engine,  in  order  to  work  with  any  economy, 
must  be  balanced,  that  is,  a  descending  empty  skip  or  cage  must 
assist  in  pulling  up  a  loaded  one.  Therefore,  except  in  mines 
of  very  small  output,  at  least  two  compartments  must  be  made 
for  hoisting  purposes.  Water  has  to  be  pumped  from  most 
mines,  escape-ways  are  necessary,  together  with  room  for  wires 
and  air-pipes,  so  that  at  least  one  more  compartment  must  be 
provided  for  these  objects.  We  have  thus  three  compartments 
as  a  sound  minimum  for  any  shaft  where  more  than  trivial  out- 
put is  required. 

Second,  there  is  a  certain  minimum  size  of  shaft  excavation 
below  which  there  is  very  little  economy  in  actual  rock-breaking.* 

*  Notes  on  the  cost  of  shafts  in  various  regions  which  have  been  per- 
sonally collected  show  a  remarkable  decrease  in  the  cost  per  cubic  foot  of 
material  excavated  with  increased  size  of  shaft.  Variations  in  skill,  in 


DEVELOPMENT  OF  MINES.  77 

In  too  confined  a  space,  holes  cannot  be  placed  to  advantage  for 
the  blast,  men  cannot  get  round  expeditiously,  and  spoil  cannot 
be  handled  readily.  The  writer's  own  experience  leads  him  to 
believe  that,  in  so  far  as  rock-breaking  is  concerned,  to  sink  a 
shaft  fourteen  to  sixteen  feet  long  by  six  to  seven  feet  wide  out- 
side the  timbers,  is  as  cheap  as  to  drive  any  smaller  size  within 
the  realm  of  consideration,  and  is  more  rapid.  This  size  of  ex- 
cavation permits  of  three  compartments,  each  about  four  to  five 
feet  inside  the  timbers. 

The  cost  of  timber,  it  is  true,  is  a  factor  of  the  size  of  shaft, 
but  the  labor  of  timbering  does  not  increase  in  the  same  ratio. 
In  any  event,  the  cost  of  timber  is  only  about  15%  of  the  actual 
shaft  cost,  even  in  localities  of  extremely  high  prices. 

Third,  three  reasons  are  rapidly  making  the  self-dumping 
skip  the  almost  universal  shaft-vehicle,  instead  of  the  old  cage 
for  cars.  First,  there  is  a  great  economy  in  labor  for  loading  into 
and  discharging  from  a  shaft;  second,  there  is  more  rapid  de- 
spatch and  discharge  and  therefore  a  larger  number  of  possible 
trips;  third,  shaft-haulage  is  then  independent  of  delays  in  ar- 
rival of  cars  at  stations,  while  tramming  can  be  done  at  any  time 
and  shaft-haulage  can  be  concentrated  into  certain  hours. 
Cages  to  carry  mine  cars  and  handle  the  same  load  as  a  skip  must 
either  be  big  enough  to  take  two  cars,  which  compels  a  much 
larger  shaft  than  is  necessary  with  skips,  or  they  must  be  double- 
decked,  which  renders  loading  arrangements  underground  costly 
to  install  and  expensive  to  work.  For  all  these  reasons,  cages  can 
be  justified  only  on  metal  mines  of  such  small  tonnage  that  time 
is  no  consideration  and  where  the  saving  of  men  is  not  to  be 
effected.  In  compartments  of  the  minimum  size  mentioned 
above  (four  to  five  feet  either  way)  a  skip  with  a  capacity  of  from 

economic  conditions,  and  in  method  of  accounting  make  data    regarding 
different  shafts  of  doubtful  value,  but  the  following  are  of  interest :  — 

In  Australia,  eight  shafts  between  10  and  11  feet  long  by  4  to  5  feet 
wide  cost  an  average  of  $1.20  per  cubic  foot  of  material  excavated.  Six 
shafts  13  to  14  feet  long  by  4  to  5  feet  wide  cost  an  average  of  $0.95  per 
cubic  foot;  seven  shafts  14  to  16  feet  long  and  5  to  7  feet  wide  cost  an 
average  of  $0.82  per  cubic  foot.  In  South  Africa,  eleven  shafts  18  to  19 
feet  long  by  7  to  8  feet  wide  cost  an  average  of  $0.82  per  cubic  foot;  five 
shafts  21  to  25  feet  long  by  8  feet  wide,  cost  $0.74;  and  seven  shafts  28 
feet  by  8  feet  cost  $0.60  per  cubic  foot. 


78  PRINCIPLES  OF  MINING. 

two  to  five  tons  can  be  installed,  although  from  two  to  three 
tons  is  the  present  rule.  Lighter  loads  than  this  involve  more 
trips,  and  thus  less  hourly  capacity,  and,  on  the  other  hand, 
heavier  loads  require  more  costly  engines.  This  matter  is 
further  discussed  under  "  Haulage  Appliances." 

We  have  therefore  as  the  economic  minimum  a  shaft  of  three 
compartments  (Fig.  9),  each  four  to  five  feet  square.  When  the 
maximum  tonnage  is  wanted  from  such  a  shaft  at  the  least 
operating  cost,  it  should  be  equipped  with  loading  bins  and  skips. 

The  output  capacity  of  shafts  of  this  size  and  equipment  will 
depend  in  a  major  degree  upon  the  engine  employed,  and  in  a  less 
degree  upon  the  hauling  depth.  The  reason  why  depth  is  a  sub- 
sidiary factor  is  that  the  rapidity  with  which  a  load  can  be  drawn 
is  not  wholly  a  factor  of  depth.  The  time  consumed  in  hoisting 
is  partially  expended  in  loading,  in  acceleration  and  retardation 
of  the  engine,  and  in  discharge  of  the  load.  These  factors  are 
constant  for  any  depth,  and  extra  distance  is  therefore  accom- 
plished at  full  speed  of  the  engine. 

Vertical  shafts  will,  other  things  being  equal,  have  greater 
capacity  than  inclines,  as  winding  will  be  much  faster  and 
length  of  haul  less  for  same  depth.  Since  engines  have,  how- 
ever, a  great  tractive  ability  on  inclines,  by  an  increase  in  the 
size  of  skip  it  is  usually  possible  partially  to  equalize  matters. 
Therefore  the  size  of  inclines  for  the  same  output  need  not  differ 
materially  from  vertical  shafts. 

The  maximum  capacity  of  a  shaft  whose  equipment  is  of  the 
character  and  size  given  above,  will,  as  stated,  decrease  some- 
what with  extension  in  depth  of  the  haulage  horizon.  At  500 
feet,  such  a  shaft  if  vertical  could  produce  70  to  80  tons  per 
hour  comfortably  with  an  engine  whose  winding  speed  was  700 
feet  per  minute.  As  men  and  material  other  than  ore  have  to  be 
handled  in  and  out  of  the  mine,  and  shaft-sinking  has  to  be  at- 
tended to,  the  winding  engine  cannot  be  employed  all  the  time 
on  ore.  Twelve  hours  of  actual  daily  ore-winding  are  all  that 
can  be  expected  without  auxiliary  help.  This  represents  a 
capacity  from  such  a  depth  of  800  to  1,000  tons  per  day.  A 
similar  shaft,  under  ordinary  working  conditions,  with  an 


DEVELOPMENT  OF  MINES.  79 

engine  speed  of  2,000  feet  per  minute,  should  from,  say,  3,000  feet 
have  a  capacity  of  about  400  to  600  tons  daily. 

It  is  desirable  to  inquire  at  what  stages  the  size  of  shaft 
should  logically  be  enlarged  in  order  to  attain  greater  capacity. 
A  considerable  measure  of  increase  can  be  obtained  by  reliev- 
ing the  main  hoisting  engine  of  all  or  part  of  its  collateral  duties. 
Where  the  pumping  machinery  is  not  elaborate,  it  is  often  pos- 
sible to  get  a  small  single  winding  compartment  into  the  gang- 
way without  materially  increasing  the  size  of  the  shaft  if  the 
haulage  compartments  be  made  somewhat  narrower  (Fig.  10). 
Such  a  compartment  would  be  operated  by  an  auxiliary  engine 
for  sinking,  handling  tools  and  material,  and  assisting  in  hand- 
ling men.  If  this  arrangement  can  be  effected,  the  productive 
time  of  the  main  engine  can  be  expanded  to  about  twenty  hours 
with  an  addition  of  about  two-thirds  to  the  output. 

Where  the  exigencies  of  pump  and  gangway  require  more 
than  two  and  one-half  feet  of  shaft  length,  the  next  stage  of 
expansion  becomes  four  full-sized  compartments  (Fig.  11). 
By  thus  enlarging  the  auxiliary  winding  space,  some  assistance 
may  be  given  to  ore-haulage  in  case  of  necessity.  The  mine  whose 
output  demands  such  haulage  provisions  can  usually  stand 
another  foot  of  width  to  the  shaft,  so  that  the  dimensions  come 
to  about  21  feet  to  22  feet  by  7  feet  to  8  feet  outside  the  timbers. 
Such  a  shaft,  with  three-  to  four-ton  skips  and  an  appropriate  en- 
gine, will  handle  up  to  250  tons  per  hour  from  a  depth  of  1,000  feet. 

The  next  logical  step  in  advance  is  the  shaft  of  five  compart- 
ments with  four  full-sized  haulage  ways  (Fig.  13),  each  of  greater 
size  than  in  the  above  instance.  In  this  case,  the  auxiliary 
engine  becomes  a  balanced  one,  and  can  be  employed  part  of  the 
time  upon  ore-haulage.  Such  a  shaft  will  be  about  26  feet  to 
28  feet  long  by  8  feet  wide  outside  the  timbers,  when  provision 
is  made  for  one  gangway.  The  capacity  of  such  shafts  can  be  up 
to  4,000  tons  a  day,  depending  on  the  depth  and  engine.  When 
very  large  quantities  of  water  are  to  be  dealt  with  and  rod-driven 
pumps  to  be  used,  two  pumping  compartments  are  sometimes 
necessary,  but  other  forms  of  pumps  do  not  require  more  than 
one  compartment,  —  an  additional  reason  for  their  use. 


80  PRINCIPLES  OF  MINING. 

For  depths  greater  than  3,000  feet,  other  factors  come  into 
play.  Ventilation  questions  become  of  more  import.  The 
mechanical  problems  on  engines  and  ropes  become  involved,  and 
their  sum-effect  is  to  demand  much  increased  size  and  a  greater 
number  of  compartments.  The  shafts  at  Johannesburg  in- 
tended as  outlets  for  workings  5,000  feet  deep  are  as  much  as  46 
feet  by  9  feet  outside  timbers. 

It  is  not  purposed  to  go  into  details  as  to  sinking  methods  or 
timbering.  While  important  matters,  they  would  unduly  pro- 
long this  discussion.  Besides,  a  multitude  of  treatises  exist  on 
these  subjects  and  cover  all  the  minutia3  of  such  work. 

Speed  of  Sinking.  —  Mines  may  be  divided  into  two  cases,  — 
those  being  developed  only,  and  those  being  operated  as  well 
as  developed.  In  the  former,  the  entrance  into  production  is 
usually  dependent  upon  the  speed  at  which  the  shaft  is  sunk. 
Until  the  mine  is  earning  profits,  there  is  a  loss  of  interest  on  the 
capital  involved,  which,  in  ninety-nine  instances  out  of  a  hundred, 
warrants  any  reasonable  extra  expenditure  to  induce  more  rapid 
progress.  In  the  case  of  mines  in  operation,  the  volume  of  ore 
available  to  treatment  or  valuation  is  generally  dependent  to  a 
great  degree  upon  the  rapidity  of  the  extension  of  workings  in 
depth.  It  will  be  demonstrated  later  that,  both  from  a  financial 
and  a  technical  standpoint,  the  maximum  development  is  the 
right  one  and  that  unremitting  extension  in  depth  is  not  only 
justifiable  but  necessary. 

Speed  under  special  conditions  or  over  short  periods  has  a 
more  romantic  than  practical  interest,  outside  of  its  value  as  a 
stimulant  to  emulation.  The  thing  that  counts  is  the  speed 
which  can  be  maintained  over  the  year.  Rapidity  of  sinking 
depends  mainly  on :  - 

a.   Whether  the  shaft  is  or  is  not  in  use  for  operating  the 

mine. 

6.   The  breaking  character  of  the  rock. 
c.   The  amount  of  water. 

The  delays  incident  to  general  carrying  of  ore  and  men  are 
such  that  the  use  of  the  main  haulage  engine  for  shaft-sinking  is 


DEVELOPMENT  OF  MINES.  81 

practically  impossible,  except  on  mines  with  small  tonnage  out- 
put. Even  with  a  separate  winch  or  auxiliary  winding-engine, 
delays  are  unavoidable  in  a  working  shaft,  especially  as  it  usually 
has  more  water  to  contend  with  than  one  not  in  use  for  operating 
the  mine.  The  writer's  own  impression  is  that  an  average  of  40 
feet  per  month  is  the  maximum  possibility  for  year  in  and  out 
sinking  under  such  conditions.  In  fact,  few  going  mines  man- 
age more  than  400  feet  a  year.  In  cases  of  clean  shaft-sinking, 
where  every  energy  is  bent  to  speed,  150  feet  per  month  have  been 
averaged  for  many  months.  Special  cases  have  occurred  where 
as  much  as  213  feet  have  been  achieved  in  a  single  month.  With 
ordinary  conditions,  1,200  feet  in  a  year  is  very  good  work.  Rock 
awkward  to  break,  and  water  especially,  lowers  the  rate  of  prog- 
ress very  materially.  Further  reference  to  speed  will  be  found 
hi  the  chapter  on  "  Drilling  Methods." 

Tunnel  Entry.  —  The  alternative  of  entry  to  a  mine  by  tunnel 
is  usually  not  a  question  of  topography  altogether,  but,  like  every- 
thing else  in  mining  science,  has  to  be  tempered  to  meet  the 
capital  available  and  the  expenditure  warranted  by  the  value 
showing. 

In  the  initial  prospecting  of  a  mine,  tunnels  are  occasionally 
overdone  by  prospectors.  Often  more  would  be  proved  by  a  few 
inclines.  As  the  pioneer  has  to  rely  upon  his  right  arm  for  hoist- 
ing and  drainage,  the  tunnel  offers  great  temptations,  even  when 
it  is  long  and  gains  but  little  depth.  At  a  more  advanced  stage 
of  development,  the  saving  of  capital  outlay  on  hoisting  and 
pumping  equipment,  at  a  time  when  capital  is  costly  to  secure, 
is  often  sufficient  justification  for  a  tunnel  entry.  But  at  the 
stage  where  the  future  working  of  ore  below  a  tunnel-level  must 
be  contemplated,  other  factors  enter.  For  ore  below  tunnel- 
level  a  shaft  becomes  necessary,  and  in  cases  where  a  tunnel 
enters  a  few  hundred  feet  below  the  outcrop  the  shaft  should 
very  often  extend  to  the  surface,  because  internal  shafts,  wind- 
ing from  tunnel-level,  require  large  excavations  to  make  room  for 
the  transfer  of  ore  and  for  winding  gear.  The  latter  must  be 
operated  by  transmitted  power,  either  that  of  steam,  water, 
electricity,  or  air.  Where  power  has  to  be  generated  on  the 


82 


PRINCIPLES   OF  MINING. 


mine,  the  saving  by  the  use  of  direct  steam,  generated  at  the 
winding  gear,  is  very  considerable.  Moreover,  the  cost  of  haul- 
age through  a  shaft  for  the  extra  distance  from  tunnel-level  to 
the  surface  is  often  less  than  the  cost  of  transferring  the  ore  and 
removing  it  through  the  tunnel.  The  load  once  on  the  winding- 
engine,  the  consumption  of  power  is  small  for  the  extra  distance, 
and  the  saving  of  labor  is  of  consequence.  On  the  other  hand, 
where  drainage  problems  arise,  they  usually  outweigh  all  other 
considerations,  for  whatever  the  horizon  entered  by  tunnel,  the 
distance  from  that  level  to  the  surface  means  a  saving  of  water- 
pumpage  against  so  much  head.  The  accumulation  of  such 
constant  expense  justifies  a  proportioned  capital  outlay.  In 
other  words,  the  saving  of  this  extra  pumping  will  annually  re- 
deem the  cost  of  a  certain  amount  of  tunnel,  even  though  it  be 
used  for  drainage  only. 

In  order  to  emphasize  the  rapidity  with  which  such  a  saving 
of  constant  expense  will  justify  capital  outlay,  one  may  tabu- 
late the  result  of  calculations  showing  the  length  of  tunnel 
warranted  with  various  hypothetical  factors  of  quantity  of 
water  and  height  of  lift  eliminated  from  pumping.  In  these 
computations,  power  is  taken  at  the  low  rate  of  $60  per  horse- 
power-year, the  cost  of  tunneling  at  an  average  figure  of  $20 
per  foot,  and  the  time  on  the  basis  of  a  ten-year  life  for  the 
mine. 

FEET  OF  TUNNEL  PAID  FOR  IN  10  YEARS  WITH  UNDER-MENTIONED 

CONDITIONS. 


FEET  OF 

100,000 

200,000 

300,000 

500,000 

1,000,000 

WATER  LIFT 

GALLONS 

GALLONS 

GALLONS 

GALLONS 

GALLONS 

AVOIDED 

PER  DIEM 

PER  DIEM 

PER  DIEM 

PER  DIEM 

PER  DIEM 

100 

600 

1,200 

1,800 

3,000 

6,000 

200 

1,200 

2,400 

3,600 

6,000 

12,000 

300 

1,800 

3,600 

5,400 

9,000 

18,000 

500 

3,000 

6,000 

9,000 

15,000 

30,000 

1,000 

6,000 

12,000 

18,000 

30,000 

60,000 

The  size  of  tunnels  where  ore-extraction  is  involved  depends 
upon  the  daily  tonnage  output-  required,  and  the  length  of 


DEVELOPMENT  OF  MINES.  83 

haul.  The  smallest  size  that  can  be  economically  driven  and 
managed  is  about  6|  feet  by  6  feet  inside  the  timbers.  Such 
a  tunnel,  with  single  track  for  a  length  of  1,000  feet,  with  one 
turn-out,  permits  handling  up  to  500  tons  a  day  with  men 
and  animals.  If  the  distance  be  longer  or  the  tonnage  greater, 
a  double  track  is  required,  which  necessitates  a  tunnel  at 
least  8  feet  wide  by  6|  feet  to  7  feet  high,  inside  the  timbers. 
There  are  tunnel  projects  of  a  much  more  impressive  order 
than  those  designed  to  operate  upper  levels  of  mines;  that 
is,  long  crosscut  tunnels  designed  to  drain  and  operate  mines 
at  very  considerable  depths,  such  as  the  Sutro  tunnel  at 
Virginia  City.  The  advantage  of  these  tunnels  is  very  great, 
especially  for  drainage,  and  they  must  be  constructed  of  large 
size  and  equipped  with  appliances  for  mechanical  haulage. 


CHAPTER  IX. 

DEVELOPMENT  OF  MINES  (Concluded). 

SUBSIDIARY  DEVELOPMENT;  —  STATIONS;  CROSSCUTS;  LEVELS; 
INTERVAL  BETWEEN  LEVELS;  PROTECTION  OF  LEVELS; 
WINZES  AND  RISES.  DEVELOPMENT  IN  THE  PROSPECTING 

NG. 
SUBSIDIARY   DEVELOPMENT. 

STATIONS,  crosscuts,  levels,  winzes,  and  rises  follow  after 
the  initial  entry.  They  are  all  expensive,  and  the  least  number 
that  will  answer  is  the  main  desideratum. 

Stations.  —  As  stations  are  the  outlets  of  the  levels  to  the 
shaft,  their  size  and  construction  is  a  factor  of  the  volume  and 
character  of  the  work  at  the  levels  which  they  are  to  serve. 
If  no  timber  is  to  be  handled,  and  little  ore,  and  this  on  cages, 
the  stations  need  be  no  larger  than  a  good  sized  crosscut. 
Where  timber  is  to  be  let  down,  they  must  be  ten  to  fifteen 
feet  higher  than  the  floor  of  the  crosscut.  Where  loading  into 
skips  is  to  be  provided  for,  bins  must  be  cut  underneath  and 
sufficient  room  be  provided  to  shift  the  mine  cars  comfortably. 
Such  bins  are  built  of  from  50  to  500  tons'  capacity  in  order 
to  contain  some  reserve  for  hoisting  purposes,  and  in 
many  cases  separate  bins  must  be  provided  on  opposite  sides 
of  the  shaft  for  ore  and  waste.  It  is  a  strong  argument  in 
favor  of  skips,  that  with  this  means  of  haulage  storage  capacity 
at  the  stations  is  possible,  and  the  hoisting  may  then  go  on 
independently  of  trucking  and,  as  said  before,  there  are  no 
idle  men  at  the  stations. 

It  is  always  desirable  to  concentrate  the  haulage  to  the 
least  number  of  levels,  for  many  reasons.  Among  them  is 
that,  where  haulage  is  confined  to  few  levels,  storage-bins  are 

84 


FIG.  15.  —  Cross-section  of  station  arrangement  for  skip-haulage  in  vertical  shaft. 


FlG.  16.  —  Cross-section  of  station  arrangement  for  skip-haulage  in  vertical  shaft, 

85 


86 


PRINCIPLES   OF  MINING. 


not  required  at  every  station.     Figures  15,  16,  17,  and  18 
illustrate  various  arrangements  of  loading  bins. 

Crosscuts.  —  Crosscuts  are  for  two  purposes,  for  roadway 
connection  of  levels  to  the  shaft  or  to  other  levels,  and  for 
prospecting  purposes.  The  number  of  crosscuts  for  roadways 
can  sometimes  be  decreased  by  making  the  connections  with 
the  shaft  at  every  second  or  even  -every  third  level,  thus  not 


FIG.  17.  —  Arrangement  of  loading  chutes  in  vertical  shaft. 

only  saving  in  the  construction  cost  of  crosscuts  and  stations, 
but  also  in  the  expenses  of  scattered  tramming.  The  matter 
becomes  especially  worth  considering  where  the  quantity 
of  ore  that'  can  thus  be  accumulated  warrants  mule  or 
mechanical  haulage.  This  subject  will  be  referred  to 
later  on. 

On  the  second  purpose  of  crosscuts,  —  that  of  prospect- 
ing, —  one  observation  merits  emphasis.  This  is,  that  the 
tendency  of  ore-fissures  to  be  formed  in  parallels  warrants 


DEVELOPMENT  OF  MINES. 


87 


more  systematic  crosscutting  into  the  country  rock  than  is 
done  in  many  mines. 


FIG.  18.  —  Cross-section  of  station  arrangement  for  skip-haulage  in  inclined  shaft. 


LEVELS. 

The  word  " level"  is  another  example  of  miners'  adap- 
tations in  nomenclature.  Its  use  in  the  sense  of  tunnels 
driven  in  the  direction  of  the  strike  of  the  deposit  has  better, 
but  less  used,  synonyms  in  the  words  " drifts"  or  " drives." 
The  term  " level"  is  used  by  miners  in  two  senses,  in  that  it 
is  sometimes  applied  to  all  openings  on  one  horizon,  cross- 
cuts included.  Levels  are  for  three  purposes,  —  for  a  stoping 


88  PRINCIPLES   OF  MINING. 

base;  for  prospecting  the  deposit;  and  for  roadways.  As 
a  prospecting  and  a  stoping  base  it  is  desirable  that  the  level 
should  be  driven  on  the  deposit ;  as  a  roadway,  that  it  should 
constitute  the  shortest  distance  between  two  points  and  be 
in  the  soundest  ground.  On  narrow,  erratic  deposits  the 
levels  usually  must  serve  all  three  purposes  at  once;  but  in 
wider  and  more  regular  deposits  levels  are  often  driven 
separately  for  roadways  from  the  level  which  forms  the  stoping 
base  and  prospecting  datum. 

There  was  a  time  when  mines  were  worked  by  driving  the 
level  on  ore  and  enlarging  it  top  and  bottom  as  far  as  the 
ground  would  stand,  then  driving  the  next  level  15  to  20  feet 
below,  and  repeating  the  operation.  This  interval  gradually 
expanded,  but  for  some  reason  100  feet  was  for  years  assumed 
to  be  the  proper  distance  between  levels.  Scattered  over 
every  mining  camp  on  earth  are  thousands  of  mines  opened 
on  this  empirical  figure,  without  consideration  of  the  reasons 
for  it  or  for  any  other  distance. 

The  governing  factors  in  determining  the  vertical  interval 
between  levels  are  the  following:  — 

a.  The  regularity  of  the  deposit. 

6.  The  effect  of  the  method  of  excavation  of  winzes  and 

rises. 
c.  The  dip  and  the  method  of  stoping. 

Regularity  of  the  Deposit.  —  From  a  prospecting  point  of 
view  the  more  levels  the  better,  and  the  interval  therefore  must 
be  determined  somewhat  by  the  character  of  the  deposit. 
In  erratic  deposits  there  is  less  risk  of  missing  ore  with  fre- 
quent levels,  but  it  does  not  follow  that  every  level  need  be 
a  through  roadway  to  the  shaft  or  even  a  stoping  base.  In 
such  deposits,  intermediate  levels  for  prospecting  alone  are 
better  than  complete  levels,  each  a  roadway.  Nor  is  it 
essential,  even  where  frequent  levels  are  required  for  a  stoping 
base,  that  each  should  be  a  main  haulage  outlet  to  the  shaft. 
In  some  mines  every  third  level  is  used  as  a  main  roadway, 
the  ore  being  poured  from  the  intermediate  ones  down  to  the 


DEVELOPMENT  OF  MINES.  89 

haulage  line.  Thus  tramming  and  shaft  work,  as  stated  before, 
can  be  concentrated. 

Effect  of  Method  of  Excavating  Winzes  and  Rises.  —  With 
hand  drilling  and  hoisting,  winzes  beyond  a  limited  depth  be- 
come very  costly  to  pull  spoil  out  of,  and  rises  too  high  become 
difficult  to  ventilate,  so  that  there  is  in  such  cases  a  limit 
to  the  interval  desirable  between  levels,  but  these  difficulties 
largely  disappear  where  air-winches  and  air-drills  are  used. 

The  Dip  and  Method  of  Stoping.  —  The  method  of  stoping 
is  largely  dependent  upon  the  dip,  and  indirectly  thus  affects 
level  intervals.  In  dips  under  that  at  which  material  will 
"flow"  in  the  stopes  —  about  45°  to  50°  —  the  interval  is 
greatly  dependent  on  the  method  of  stope-transport.  Where 
ore  is  to  be  shoveled  from  stopes  to  the  roadway,  the  levels 
must  be  comparatively  close  together.  Where  deposits  are  very 
flat,  under  20°,  and  walls  fairly  sound,  it  is  often  possible  to 
use  a  sort  of  long  wall  system  of  stoping  and  to  lay  tracks  in 
the  stopes  with  self-acting  inclines  to  the  levels.  In  such 
instances,  the  interval  can  be  expanded  to  250  or  even  400 
feet.  In  dips  between  20°  and  45°,  tracks  are  not  often  pos- 
sible, and  either  shoveling  or  " bumping  troughs"*  are  the 
only  help  to  transport.  With  shoveling,  intervals  of  100  feet  f 
are  most  common,  and  with  troughs  the  distance  can  be  ex- 
panded up  to  150  or  175  feet. 

In  dips  of  over  40°  to  50°,  depending  on  the  smoothness 
of  the  foot  wall,  the  distance  can  again  be  increased,  as 
stope-transport  is  greatly  simplified,  since  the  stope  materials 
fall  out  by  gravity.  In  timbered  stopes,  in  dips  over  about 
45°,  intervals  of  150  to  200  feet  are  possible.  In  filled  stopes 
intervals  of  over  150  feet  present  difficulties  in  the  maintenance 
of  ore-passes,  for  the  wear  and  tear  of  longer  use  often  breaks 
the  timbers.  In  shrinkage-stopes,  where  no  passes  are  to  be 
maintained  and  few  winzes  put  through,  the  interval  is  some- 
times raised  to  250  feet.  The  subject  is  further  discussed 
under  "  Stoping." 

Another  factor  bearing  on    level  intervals  is  the  needed 

*  Page  136.  f  Intervals  given  are  measured  on  the  dip. 


90 


PRINCIPLES   OF  MINING. 


insurance  of  sufficient  points  of  stoping  attack  to  keep  up 
a  certain  output.  This  must  particularly  influence  the 
manager  whose  mine  has  but  little  ore  in  reserve. 

Protection  of  Levels.  —  Until  recent  years,  timbering  and 
occasional  walling  was  the  only  method  for  the  support  of 
the  roof,  and  for  forming  a  platform  for  a  stoping  base.  Where 
the  rock  requires  no  support  sublevels  can  be  used  as  a  stoping 
base,  and  timbering  for  such  purpose  avoided  altogether 


FIG.  19. 

(Figs.  38,  39,  42).  In  such  cases  the  main  roadway  can  then 
be  driven  on  straight  lines,  either  in  the  walls  or  in  the  ore, 
and  used  entirely  for  haulage.  The  subheading  for  a  stoping 
base  is  driven  far  enough  above  or  below  the  roadway  (de- 
pending on  whether  overhand  or  underhand  stoping  is  to  be 
used)  to  leave  a  supporting  pillar  which  is  penetrated  by  short 
passes  for  ore.  In  overhand  stopes,  the  ore  is  broken  directly 
on  the  floor  of  an  upper  sublevel;  and  in  underhand  stopes, 
broken  directly  from  the  bottom  of  the  sublevel.  The  method 


DEVELOPMENT  OF  MINES.  91 

entails  leaving  a  pillar  of  ore  which  can  be  recovered  only 
with  difficulty  in  mines  where  stope-support  is  necessary. 
The  question  of  its  adoption  is  then  largely  one  of  the  com- 
parative cost  of  timbering,  the  extra  cost  of  the  sublevel, 
and  the  net  value  of  the  ore  left.  In  bad  swelling  veins,  or 
badly  crushing  walls,  where  constant  repair  to  timbers  would 
be  necessary,  the  use  of  a  sublevel  is  a  most  useful  alternative. 
It  is  especially  useful  with  stopes  to  be  left  open  or  worked 
by  shrinkage-stoping  methods. 

If  the  haulage  level,  however,  is  to  be  the  stoping  base, 
some  protection  to  the  roadway  must  be  provided.  There  are 
three  systems  in  use,  —  by  wood  stulls  or  sets  (Figs.  19,  30,  43), 
by  dry-walling  with  timber  caps  (Fig.  35),  and  in  some  localities 
by  steel  sets.  Stulls  are  put  up  in  various  ways,  and,  as  their 
use  entails  the  least  difficulty  in  taking  the  ore  out  from 
beneath  the  level,  they  are  much  favored,  but  are  applicable 
only  in  comparatively  narrow  deposits. 

WINZES   AND   RISES. 

These  two  kinds  of  openings  for  connecting  two  horizons 
in  a  mine  differ  only  in  their  manner  of  construction.  A 
winze  is  sunk  underhand,  while  a  rise  is  put  up  overhand. 
When  the  connection  between  levels  is  completed,  a  miner 
standing  at  the  bottom  usually  refers  to  the  opening  as  a  rise, 
and  when  he  goes  to  the  top  he  calls  it  a  winze.  This  con- 
fusion in  terms  makes  it  advisable  to  refer  to  all  such  com- 
pleted openings  as  winzes,  regardless  of  how  they  are 
constructed. 

In  actual  work,  even  disregarding  water,  it  costs  on  the 
average  about  30%  less  to  raise  than  to  sink  such  openings, 
for  obviously  the  spoil  runs  out  or  is  assisted  by  gravity  in 
one  case,  and  in  the  other  has  to  be  shoveled  and  hauled  up. 
Moreover,  it  is  easier  to  follow  the  ore  in  a  rise  than  in  a  winze. 
It  usually  happens,  however,  that  in  order  to  gain  time  both 
things  are  done,  and  for  prospecting  purposes  sinking  is 
necessary. 


92  PRINCIPLES  OF  MINING. 

The  number  of  winzes  required  depends  upon  the  method 
of  stoping  adopted,  and  is  mentioned  under  "  Stoping."  After 
stoping,  the  number  necessary  to  be  maintained  open  depends 
upon  the  necessities  of  ventilation,  of  escape,  and  of  passage- 
ways for  material  to  be  used  below.  Where  stopes  are  to  be 
filled  with  waste,  more  winzes  must  be  kept  open  than  when 
other  methods  are  used,  and  these  winzes  must  be  in  sufficient 
alignment  to  permit  the  continuous  flow  of  material  down 
past  the  various  levels.  In  order  that  the  winzes  should 
deliver  timber  and  filling  to  the  most  advantageous  points, 
they  should,  in  dipping  ore-bodies,  be  as  far  as  possible  on 
the  hanging  wall  side. 

DEVELOPMENT    IN   THE    EARLY    PROSPECTING    STAGE. 

The  prime  objects  in  the  prospecting  stage  are  to  expose 
the  ore  and  to  learn  regarding  the  ore-bodies  something  of 
their  size,  their  value,  metallurgical  character,  location,  dip, 
strike,  etc.,  —  so  much  at  least  as  may  be  necessary  to  deter- 
mine the  works  most  suitable  for  their  extraction  or  values 
warranting  purchase.  In  outcrop  mines  there  is  one  rule,  and 
that  is  "  follow  the  ore."  Small  temporary  inclines  following 
the  deposit,  even  though  they  are  eventually  useless,  are  nine 
times  out  of  ten  justified. 

In  prospecting  deep-level  projects,  it  is  usually  necessary 
to  lay  out  work  which  can  be  subsequently  used  in  operating 
the  mine,  because  the  depth  involves  works  of  such  consider- 
able scale,  even  for  prospecting,  that  the  initial  outlay  does  not 
warrant  any  anticipation  of  revision.  Such  works  have  to  be 
located  and  designed  after  a  study  of  the  general  geology  as 
disclosed  in  adjoining  mines.  Practically  the  only  method  of 
supplementing  such  information  is  by  the  use  of  churn-  and 
diamond-drills. 

Drilling.  —  Churn-drills  are  applicable  only  to  compara- 
tively shallow  deposits  of  large  volume.  They  have  an 
advantage  over  the  diamond  drill  in  exposing  a  larger  section 
and  ifi  their  application  to  loose  material ;  but  inability  to  de- 


DEVELOPMENT  OF  MINES.  93 

termine  the  exact  horizon  of  the  spoil  does  not  lend  them  to 
narrow  deposits,  and  in  any  event  results  are  likely  to  be 
misleading  from  the  finely  ground  state  of  the  spoil.  They  are, 
however,  of  very  great  value  for  preliminary  prospecting  to 
shallow  horizons. 

Two  facts  in  diamond-drilling  have  to  be  borne  in  mind  : 
the  indication  of  values  is  liable  to  be  misleading,  and  the 
deflection  of  the  drill  is  likely  to  carry  it  far  away  from  its 
anticipated  destination.  A  diamond-drill  secures  a  small 
section  which  is  sufficiently  large  to  reveal  the  geology,  but 
the  values  disclosed  in  metal  mines  must  be  accepted  with 
reservations.  The  core  amounts  to  but  a  little  sample  out 
of  possibly  large  amounts  of  ore,  which  is  always  of  variable 
character,  and  the  core  is  most  unlikely  to  represent  the 
average  of  the  deposit.  Two  diamond-drill  holes  on  the 
Oroya  Brownhill  mine  both  passed  through  the  ore-body. 
One  apparently  disclosed  unpayable  values,  the  other  seem- 
ingly showed  ore  forty  feet  in  width  assaying  $80  per  ton. 
Neither  was  right.  On  the  other  hand,  the  predetermination 
of  the  location  of  the  ore-body  justified  expenditure.  A 
recent  experiment  at  Johannesburg  of  placing  a  copper 
wedge  in  the  hole  at  a  point  above  the  ore-body  and  deflect- 
ing the  drill  on  reintroducing  it,  was  successful  in  giving  a 
second  section  of  the  ore  at  small  expense. 

The  deflection  of  diamond-drill  holes  from  the  starting  angle 
is  almost  universal.  It  often  amounts  to  a  considerable 
wandering  from  the  intended  course.  The  amount  of  such 
deflection  varies  with  no  seeming  rule,  but  it  is  probable  that 
it  is  especially  affected  by  the  angle  at  which  stratification 
or  lamination  planes  are  inclined  to  the  direction  of  the  hole. 
A  hole  has  been  known  to  wander  in  a  depth  of  1,500  feet  more 
than  500  feet  from  the  point  intended.  Various  instruments 
have  been  devised  for  surveying  deep  holes,  and  they  should 
be  brought  into  use  Before  works  are  laid  out  on  the  basis  of 
diamond-drill  results,  although  none  of  the  inventions  are 
entirely  satisfactory. 


CHAPTER  X. 
STOPING. 

METHODS  OF  ORE-BREAKING;  UNDERHAND  STOPESJ  OVERHAND 
STOPES;  COMBINED  STOPE.  VALUING  ORE  IN  COURSE  OF 
BREAKING. 

THERE  is  a  great  deal  of  confusion  in  the  application  of  the 
word  "  stoping."  It  is  used  not  only  specifically  to  mean  the 
actual  ore-breaking,  but  also  in  a  general  sense  to  indicate  all 
the  operations  of  ore-breaking,  support  of  excavations,  and  trans- 
portation between  levels.  It  is  used  further  as  a  noun  to  desig- 
nate the  hole  left  when  the  ore  is  taken  out.  Worse  still,  it  is 
impossible  to  adhere  to  miners'  terms  without  employing  it  in 
every  sense,  trusting  to  luck  and  the  context  to  make  the  mean- 
ing clear. 

The  conditions  which  govern  the  method  of  stoping  are  in 
the  main:  — 

a.   The  dip. 

6.   The  width  of  the  deposit. 

c.  The  character  of  the  walls. 

d.  The  cost  of  materials. 

e.  The  character  of  the  ore. 

Every  mine,  and  sometimes  every  stope  in  a  mine,  is  a  prob- 
lem special  to  itself.  Any  general  consideration  must  therefore 
be  simply  an  inquiry  into  the  broad  principles  which  govern 
the  adaptability  of  special  methods.  A  logical  arrangement  of 
discussion  is  difficult,  if  not  wholly  impossible,  because  the 
factors  are  partially  interdependent  and  of  varying  importance. 

For  discussion  the  subject  may  be  divided  into: 

1.  Methods  of  ore-breaking. 

2.  Methods  of  supporting  excavation. 

3.  Methods  of  transport  in  stopes. 

94 


STOPING. 


95 


METHODS    OF   ORE-BREAKING. 


The  manner  of  actual  ore-breaking  is  to  drill  and  blast  off 
slices  from  the  block  of  ground  under  attack.  As  rock  ob- 
viously breaks  easiest  when  two  sides  are  free,  that  is,  when 
corners  can  be  broken  off,  the  detail  of  management  for  blasts 


FIG.  20. 

is  therefore  to  set  the  holes  so  as  to  preserve  a  corner  for  the 
next  cut ;  and  as  a  consequence  the  face  of  the  stope  shapes  into 
a  series  of  benches  (Fig.  22), —  inverted  benches  in  the  case  of 
overhand  stopes  (Figs.  20,  21).  The  size  of  these  benches  will 
in  a  large  measure  depend  on  the  depth  of  the  holes.  In  wide 
stopes  with  machine-drills  they  vary  from  7  to  10  feet;  in 
narrow  stopes  with  hand-holes,  from  two  to  three  feet. 

The  position  of  the  men   in  relation  to  the  working  face 


96 


PRINCIPLES  OF  MINING. 


gives  rise  to  the  usual  primary  classification  of  the  methods  of 
stoping.     They  are:  — 

1.  Underhand  stopes, 

2.  Overhand  stopes, 

3.  Combined  stopes. 

These  terms  originated  from  the  direction  of  the  drill-holes, 
but  this  is  no  longer  a  logical  basis  of  distinction,  for  under- 


I    I     I     I 


FIG.  21. 

hand  holes  in  overhand  stopes,  —  as  in  rill-stoping,  —  are  used 
entirely  in  some  mines  (Fig.  21). 

Underhand  Stopes.  —  Underhand  stopes  are  those  in  which 
the  ore  is  broken  downward  from  the  levels.  Inasmuch  as  this 
method  has  the  advantage  of  allowing  the  miner  to  strike  his 
blows  downward  and  to  stand  upon  the  ore  when  at  work,  it 
was  almost  universal  before  the  invention  of  powder,  and  was 


STOPING. 


97 


applied  more  generally  before  the  invention  of  machine-drills 
than  since.  It  is  never  rightly  introduced  unless  the  stope  is 
worked  back  from  winzes  through  which  the  ore  broken  can  be 
let  down  to  the  level  below,  as  shown  in  Figures  22  and  23. 

This  system  can  be  advantageously  applied  only  in  the  rare 
cases  in  which  the  walls  require  little  or  no  support,  and  where 
very  little  or  no  waste  requiring  separation  is  broken  with  the 
ore  in  the  stopes.  To  support  the  walls  in  bad  ground  in  under- 


FIG.  22. 

hand  stopes  would  be  far  more  costly  than  with  overhand 
stopes,  for  square-set  timbering  would  be  most  difficult  to  in- 
troduce, and  to  support  the  walls  with  waste  and  stulls  would 
be  even  more  troublesome.  Any  waste  broken  must  needs  be 
thrown  up  to  the  level  above  or  be  stored  upon  specially  built 

-again  a  costly  proceeding. 
A  further  drawback  lies  in  the  fact  that  the  broken  ore. 


98 


PRINCIPLES   OF  MINING. 


follows  down  the  face  of  the  stope,  and  must  be  shoveled  off 
each  bench.  It  thus  all  arrives  at  a  single  point,  —  the  winze, 
—  and  must  be  drawn  from  a  single  ore-pass  into  the  level. 
This  usually  results  not  only  in  more  shoveling  but  in  a  con- 
gestion at  the  passes  not  present  in  overhand  stoping,  for  with 
that  method  several  chutes  are  available  for  discharging  ore 
into  the  levels.  Where  the  walls  require  no  support  and  no 
selection  is  desired  in  the  stopes,  the  advantage  of  the  men 
standing  on  the  solid  ore  to  work,  and  of  having  all  down  holes 
and  therefore  drilled  wet,  gives  this  method  a  distinct  place. 
In  using  this  system,  in  order  to  protect  the  men,  a  pillar  is 


FIG.  23.  —  Longitudinal  section  of  an  underhand  stope. 

often  left  under  the  level  by  driving  a  sublevel,  the  pillar  being 
easily  recoverable  later.  The  method  of  sublevels  is  of  ad- 
vantage largely  in  avoiding  the  timbering  of  levels. 

Overhand  Stopes.  —  By  far  the  greatest  bulk  of  ore  is  broken 
overhand,  that  is  broken  upward  from  one  level  to  the  next 
above.  There  are  two  general  forms  which  such  stopes  are 
given,  —  " horizontal"  and  "rill." 

The  horizontal  "flat-back"  or  "long-wall"  stope,  as  it  is 
variously  called,  shown  in  Figure  24,  is  operated  by  breaking 
the  ore  in  slices  parallel  with  the  levels.  In  rill-stoping  the  ore 
is  cut  back  from  the  winzes  in  such  a  way  that  a  pyramid- 
shaped  room  is  created,  with  its  apex  in  the  winze  and  its  base 


STOPING. 


99 


at  the  level  (Figs.  25  and  26).     Horizontal  or  flat-backed  stopes 
can  be  applied  to  almost  any  dip,  while  "  rill-stoping "  finds  its 


LEVEL 


FIG.  24. —  Horizontal-cut  overhand  stope  —  longitudinal  section. 

most  advantageous  application  where  the  dip  is  such  that  the 
ore  will  "run,"  or  where  it  can  be  made  to  "run"  with  a  little 
help.  The  particular  application  of  the  two  systems  is  de- 


FIG.  25.  —  Rill-cut  overhand  stope  —  longitudinal  section. 

• 

pendent  not  only  on  the  dip  but  on  the  method  of  supporting 
the  excavation  and  the  ore.    With  rill-stoping,  it  is  possible  to 


100 


PRINCIPLES   OF  MIXING. 


cut  the  breaking  benches  back  horizontally  from  the  winzes 
(Fig.  25),  or  to  stagger  the  cuts  in  such  a  manner  as  to  take  the 
slices  in  a  descending  angle  (Figs.  21  and  26). 

In  the  "rill"  method  of  incline  cuts,  all  the  drill-holes  are 
"down"  holes  (Fig.  21),  and  can  be  drilled  wet,  while  in  hori- 
zontal cuts  or  flat-backed  stopes,  at  least  part  of  the  holes 
must  be  "uppers"  (Fig.  20).  Aside  from  the  easier  and 
cheaper  drilling  and  setting  up  of  machines  with  this  kind  of 
"cut,"  there  is  no  drill  dust,  —  a  great  desideratum  in  these 
days  of  miners'  phthisis.  A  further  advantage  in  the  "rill "  cut 


FIG.  26.  —  Rill-cut  overhand  stope  —  longitudinal  section. 

arises  in  cases  where  horizontal  jointing  planes  run  through 
the  ore  of  a  sort  from  which  unduly  large  masses  break  away 
in  "flat-back"  stopes.  By  the  descending  cut  of  the  "rill" 
method  these  calamities  can  be  in  a  measure  avoided.  In  cases 
of  dips  over  40°  the  greatest  advantage  in  "rill"  stoping  arises 
from  the  possibility  of  pouring  filling  or  timber  into  the  stope 
from  above  with  less  handling,  because  the  ore  and  material 
will  run  down  the  sides  of  the  pyramid  (Figs.  32  and  34).  Thus 
not  only  is  there  less  shoveling  required,  but  fewer  ore-passes 
and  a  less  number  of  preliminary  winzes  are  necessary,  and  a 
wider  level  interval  is  possible.  This  matter  will  be  gone  into 
more  fully  later. 


STOPING. 


101 


Combined  Stopes.  —  A  combined  stope  is  made  by  the  co- 
incident working  of  the  underhand  and  "rill"  method  (Fig.  27). 
This  order  of  stope  has  the  same  limitations  in  general  as  the 
underhand  kind.  For  flat  veins  with  strong  walls,  it  has  a 
great  superiority  in  that  the  stope  is  carried  back  more  or  less 
parallel  with  the  winzes,  and  thus  broken  ore  after  blasting  lies 
in  a  line  on  the  gradient  of  the  stope.  It  is,  therefore,  con- 
veniently placed  for  mechanical  stope  haulage.  A  further  ad- 
vantage is  gained  in  that  winzes  may  be  placed  long  distances, 
apart,  and  that  men  are  not  required,  either  when  at  work  or 


FIG.  27.  —  Longitudinal  section  of  a. combined  stope. 

passing  to  and  from  it,  to  be  ever  far  from  the  face,  and  they 
are  thus  in  the  safest  ground,  so  that  timber  and  filling  pro- 
tection which  may  be  otherwise  necessary  is  not  required.  This 
method  is  largely  used  in  South  Africa. 

Minimum  Width  of  Stopes.  —  The  minimum  stoping  width 
which  can  be  consistently  broken  with  hand-holes  is  about  30 
inches,  and  this  only  where  there  is  considerable  dip  to  the  ore. 
This  space  is  so  narrow  that  it  is  of  doubtful  advantage  in  any 
case,  and  40  inches  is  more  common  in  narrow  mines,  especially 
where  worked  with  white  men.  Where  machine-drills  are  used 
about  4  feet  is  the  minimum  width  feasible. 

Resuing.  —  In  very  narrow  veins  where  a  certain  amount  of 
wall-rock  must  be  broken  to  give  working  space,  it  pays  under 


102  PRINCIPLES  OF  MINING. 

some  circumstances  to  advance  the  stope  into  the  wall-rock 
ahead  of  the  ore,  thus  stripping  the  ore  and  enabling  it  to  be 
broken  separately.  This  permits  of  cleaner  selection  of  the 
ore;  but  it  is  a  problem  to  be  worked  out  in  each  case,  as  to 
whether  rough  sorting  of  some  waste  in  the  stopes,  or  further 
sorting  at  surface  with  inevitable  treatment  of  some  waste  rock, 
is  more  economical  than  separate  stoping  cuts  and  inevitably 
wider  stopes. 

Valuing  Ore  in  Course  of  Breaking.  —  There  are  many  ores 
whose  payability  can  be  determined  by  inspection,  but  there 
are  many  of  which  it  cannot.  Continuous  assaying  is  in  the 
latter  cases  absolutely  necessary  to  avoid  the  treatment  of 
valueless  material.  In  such  instances,  sampling  after  each 
stoping-cut  is  essential,  the  unprofitable  ore  being  broken  down 
and  used  as  waste.  Where  values  fade  into  the  walls,  as  in  im- 
pregnation deposits,  the  width  of  stopes  depends  upon  the  limit 
of  payability.  In  these  cases,  drill-holes  are  put  into  the  walls 
and  the  drillings  assayed.  If  the  ore  is  found  profitable,  the  holes 
are  blasted  out.  The  gauge  of  what  is  profitable  in  such  situations 
is  not  dependent  simply  upon  the  average  total  working  costs  of 
the  mine,  for  ore  in  that  position  can  be  said  to  cost  nothing  for 
development  work  and  administration;  moreover,  it  is  usually 
more  cheaply  broken  than  the  average  breaking  cost,  men  and 
machines  being  already  on  the  spot. 


CHAPTER  XL 

METHODS  OF  SUPPORTING  EXCAVATION. 

TIMBERING ;  FILLING  WITH  WASTE ;  FILLING  WITH  BROKEN  ORE  J 
PILLARS  OF  ORE;  ARTIFICIAL  PILLARS;  CAVING  SYSTEM. 

MOST  slopes  require  support  to  be  given  to  the  walls  and  often 
to  the  ore  itself.  Where  they  do  require  support  there  are  five 
principal  methods  of  accomplishing  it.  The  application  of  any 
particular  method  depends  upon  the  dip,  width  of  ore-body,  char- 
acter of  the  ore  and  walls,  and  cost  of  materials.  The  various 
systems  are  by :  - 

1.  Timbering. 

2.  Filling  with  waste. 

3.  Filling  with  broken  ore  subsequently  withdrawn. 

4.  Pillars  of  ore. 

5.  Artificial  pillars  built  of  timbers  and  waste. 

6.  Caving. 

Timbering.  —  At  one  time  timbering  was  the  almost  uni- 
versal means  of  support  in  such  excavations,  but  gradually  various 
methods  for  the  economical  application  of  waste  and  ore  itself 
have  come  forward,  until  timbering  is  fast  becoming  a  secondary 
device.  Aside  from  economy  in  working  without  it,  the  dangers 
of  creeps,  or  crushing,  and  of  fires  are  sufficient  incentives  to  do 
away  with  wood  as  far  as  possible. 

There  are  three  principal  systems  of  timber  support  to  excava- 
tions, —  by  stulls,  square-sets,  and  cribs. 

Stulls  are  serviceable  only  where  the  deposit  is  so  narrow  that 
the  opening  can  be  bridged  by  single  timbers  between  wall  and 
wall  (Figs.  28  and  43).  This  system  can  be  applied  to  any  dip  and 
is  most  useful  in  narrow  deposits  where  the  walls  are  not  too  heavy. 
Stulls  in  inclined  deposits  are  usually  set  at  a  slightly  higher 

103 


104 


PRINCIPLES   OF  MINING. 


angle  than  that  perpendicular  to  the  walls,  in  order  that  the 
vertical  pressure  of  the  hanging  wall  will  serve  to  tighten  them  in 


FIG.  28.  —  Longitudinal  section  of  stull-supported  stope. 

position.  The  "stull"  system  can,  in  inclined  deposits,  be 
further  strengthened  by  building  waste  pillars  against  them,  in 
which  case  the  arrangement  merges  into  the  system  of  artificial 
pillars. 

Square-sets  (Figs.  29  and  30),  that  is,  trusses  built  in  the  open- 
ing as  the  ore  is  removed,  are  applicable  to  almost  any  dip  or  width 


FIG.  29.  —  Longitudinal  section  showing  square-set  timbering. 


of  ore,  but  generally  are  applied  only  in  deposits  too  wide,  or  to 
rock  too  heavy,  for  stulls.    Such  trusses  are  usually  constructed  on 


METHODS  OF  SUPPORTING  EXCAVATION. 


105 


vertical  and  horizontal  lines,  and  while  during  actual  ore-breaking 
the  strains  are  partially  vertical,  ultimately,  however,  when  the 
weight  of  the  walls  begins  to  be  felt,  these  strains,  except  in 
vertical  deposits,  come  at  an  angle  to  lines  of  strength  in  the 
trusses,  and  therefore  timber  constructions  of  this  type  present 


\ 


FIG.  30.  —  Square-set  timbering  on  inclined  ore-body.     Showing  ultimate 
strain  on  timbers. 

little  ultimate  resistance  (Fig.  30).  Square-set  timbers  are 
sometimes  set  to  present  the  maximum  resistance  to  the  direction 
of  strain,  but  the  difficulties  of  placing  them  in  position  and 
variations  in  the  direction  of  strain  on  various  parts  of  the  stope 
do  not  often  commend  the  method.  As  a  general  rule  square-sets 
on  horizontal  lines  answer  well  enough  for  the  period  of  actual 
ore-breaking.  The  crushing  or  creeps  is  usually  some  time  later ; 


106 


PRINCIPLES  OF  MINING. 


and  if  the  crushing  may  damage  the  whole  mine,  their  use  is 
fraught  with  danger.  Reinforcement  by  building  in  waste  is 
often  resorted  to.  When  done  fully,  it  is  difficult  to  see  the  util- 
ity of  the  enclosed  timber,  for  entire  waste-filling  would  in  most 
cases  be  cheaper  and  equally  efficient. 

There  is  always,  with  wood  constructions,  as  said  before,  the 
very  pertinent  danger  of  subsequent  crushing  and  of  subsidence 
in  after  years,  and  the  great  risk  of  fires.  Both  these  disasters 


FIG.  31.  —  "Cribs." 

have  cost  Comstock  and  Broken  Hill  mines,  directly  or  indirectly, 
millions  of  dollars,  and  the  outlay  on  timber  and  repairs  one  way 
or  another  would  have  paid  for  the  filling  system  ten  times  over. 
There  are  cases  where,  by  virtue  of  the  cheapness  of  timber, 
" square-setting"  is  the  most  economical  method.  Again,  there 
are  instances  where  the  ore  lies  in  such  a  manner  —  particularly  in 
limestone  replacements  —  as  to  preclude  other  means  of  support. 
These  cases  are  being  yearly  more  and  more  evaded  by  the  in- 
genuity of  engineers  in  charge.  The  author  believes  it  soon  will 


METHODS  OF  SUPPORTING  EXCAVATION.  107 

be  recognized  that  the  situation  is  rare  indeed  where  complete 
square-setting  is  necessarily  without  an  economical  alternative. 
An  objection  is  sometimes  raised  to  filling  in  favor  of  timber,  in 
that  if  it  become  desirable  to  restope  the  walls  for  low-grade  ore 
left  behind,  such  stopes  could  only  be  entered  by  drawing  the 
filling,  with  consequent  danger  of  total  collapse.  Such  a  con- 
tingency can  be  provided  for  in  large  ore-bodies  by  installing  an 
outer  shell  of  sets  of  timber  around  the  periphery  of  the  stope  and 
filling  the  inside  with  waste.  If  the  crushing  possibilities  are  too 
great  for  this  method  then,  the  subsequent  recovery  of  ore  is 
hopeless  in  any  event.  In  narrow  ore-bodies  with  crushing  walls 
recovery  of  ore  once  left  behind  is  not  often  possible. 

The  third  sort  of  timber  constructions  are  cribs,  a  "log-house" 
sort  of  structure  usually  filled  with  waste,  and  more  fully  dis- 
cussed under  artificial  pillars  (Fig.  31).  The  further  compara- 
tive merits  of  timbering  with  other  methods  will  be  analyzed 
as  the  different  systems  are  described. 

Filling  with  Waste.  —  The  system  of  filling  stope-excava- 
tions  completely  with  waste  in  alternating  progress  with  ore- 
breaking  is  of  wide  and  increasingly  general  application  (Figs. 
32,  33,  34,  35). 

Although  a  certain  amount  of  waste  is  ordinarily  available 
in  the  stopes  themselves,  or  from  development  work  in  the 
mine,  such  a  supply  must  usually  be  supplemented  from  other 
directions.  Treatment  residues  afford  the  easiest  and  cheapest 
handled  material.  Quarried  rock  ranks  next,  and  in  default  of 
any  other  easy  supply,  materials  from  crosscuts  driven  into  the 
stope- walls  are  sometimes  resorted  to. 

In  working  the  system  to  the  best  advantage,  the  winzes 
through  the  block  of  ore  under  attack  are  kept  in  alignment 
with  similar  openings  above,  in  order  that  filling  may  be  poured 
through  the  mine  from  the  surface  or  any  intermediate  point. 
Winzes  to  be  used  for  filling  should  be  put  on  the  hanging-wall 
side  of  the  area  to  be  filled,  for  the  filling  poured  down  will  then 
reach  the  foot- wall  side  of  the  stopes  with  a  minimum  of  hand- 
ling. In  some  instances,  one  special  winze  is  arranged  for  pass- 
ing all  filling  from  the  surface  to  a  level  above  the  principal  stop- 


FIG.  32. —  Longitudinal  section.     Rill  stope  filled  with  waste. 


FIG.  33.  — Longitudinal  section.    Horizontal  stope  filled  with  waste. 


108 


METHODS  OF  SUPPORTING  EXCAVATION. 


109 


ing  operations;  and  it  is  then  distributed  along  the  levels  into  the 
winzes,  and  thus  to  the  operating  stopes,  by  belt-conveyors. 

In  this  system  of  stope  support  the  ore  is  broken  at  intervals 
alternating  with  filling.  If  there  is  danger  of  much  loss  from 
mixing  broken  ore  and  filling,  "sollars"  of  boards  or  poles  are 
laid  on  the  waste.  If  the  ore  is  very  rich,  old  canvas  or  cowhides 


LEVEL 


LEVEL 


LEVEL 


FIG.  34.  —  Longitudinal  section.     Waste-filled  stope  with  dry- walling  of  levels  and 


are  sometimes  put  under  the  boards.  Before  the  filling  interval, 
the  ore  passes  are  built  close  to  the  face  above  previous  filling 
and  their  tops  covered  temporarily  to  prevent  their  being  filled 
with  running  waste.  If  the  walls  are  bad,  the  filling  is  kept 
close  to  the  face.  If  the  unbroken  ore  requires  support,  short 
stulls  set  on  the  waste  (as  in  Fig.  39)  are  usually  sufficient  until 
the  next  cut  is  taken  off,  when  the  timber  can  be  recovered.  If 
stulls  are  insufficient,  cribs  or  bulkheads  (Fig.  31)  are  also  used 
and  often  buried  in  the  filling. 


110 


PRINCIPLES   OF  MINING. 


Both  flat-backed  and  rill-stope  methods  of  breaking  are  em- 
ployed in  conjunction  with  filled  stopes.  The  advantages  of 
the  rill-stopes  are  so  patent  as  to  make  it  difficult  to  understand 
why  they  are  not  universally  adopted  when  the  dip  permits  their 
use  at  all.  In  rill-stopes  (Figs.  32  and  34)  the  waste  flows  to  its 
destination  with  a  minimum  of  handling.  Winzes  and  ore-passes 


VEL 


LEVEL 


FIG.  35.  — Cross-section  of  Fig.  34  on  line  A-B. 

are  not  required  with  the  same  frequency  as  in  horizontal  break- 
ing, and  the  broken  ore  always  lies  on  the  slope  towards  the  passes 
and  is  therefore  also  easier  to  shovel.  In  flat-backed  stopes  (Fig. 
33)  winzes  must  be  put  in  every  50  feet  or  so,  while  in  rill-stopes 
they  can  be  double  this  distance  apart.  The  system  is  appli- 
cable by  modification  to  almost  any  width  of  ore.  It  finds  its 
most  economical  field  where  the  dip  of  the  stope  floor  is  over  45°, 
when  waste  and  ore,  with  the  help  of  the  "rill,"  will  flow  to  their 
destination.  For  dips  from  under  about  45°  to  about  30°  or  35°, 


METHODS   OF  SUPPORTING   EXCAVATION.  Ill 

where  the  waste  and  ore  will  not  "flow"  easily,  shoveling  can  be 
helped  by  the  use  of  the  "rill"  system  and  often  evaded  alto- 
gether, if  flow  be  assisted  by  a  sheet-iron  trough  described  in 
the  discussion  of  stope  transport.  Further  saving  in  shoveling  can 
be  gained  in  this  method,  by  giving  a  steeper  pitch  to  the  filling 
winzes  and  to  the  ore-passes,  by  starting  them  from  crosscuts  in 
the  wall,  and  by  carrying  them  at  greater  angles  than  the  pitch 
of  the  ore  (Fig.  36).  These  artifices  combined  have  worked  out 
most  economically  on  several  mines  within  the  writer's  experi- 


FIG.  36.  —  Cross-section  showing  method  of  steepening  winzes  and  ore  passes. 

ence,  with  the  dip  as  flat  as  30°.  For  very  flat  dips,  where  filling 
is  to  be  employed,  rill-stoping  has  no  advantage  over  flat-backed 
cuts,  and  in  such  cases  it  is  often  advisable  to  assist  stope  trans- 
port by  temporary  tracks  and  cars  which  obviously  could  not  be 
worked  on  the  tortuous  contour  of  a  rill-stope,  so  that  for  dips 
under  30°  advantage  lies  with  "flat-backed"  ore-breaking. 

On  very  wide  ore-bodies  where  the  support  of  the  standing 
ore  itself  becomes  a  great  problem,  the  filling  system  can  be 
applied  by  combining  it  with  square-setting.  In  this  case  the 
stopes  are  carried  in  panels  laid  out  transversally  to  the  strike 
as  wide  as  the  standing  strength  of  the  ore  permits.  On  both 
sides  of  each  panel  a  fence  of  lagged  square-sets  is  carried  up  and 


112  PRINCIPLES  OF  MINING. 

the  area  between  is  filled  with  waste.  The  panels  are  stoped  out 
alternately.  The  application  of  this  method  at  Broken  Hill 
will  be  described  later.  (See  pages  120  and  Figs.  41  and  42.)  The 
same  type  of  wide  ore-body  can  be  managed  also  on  the  filling 
system  by  the  use  of  frequent  " bulkheads"  to  support  the  ore 
(Fig.  31). 

Compared  with  timbering  methods,  filling  has  the  great 
advantage  of  more  effective  support  to  the  mine,  less  danger  of 
creeps,  and  absolute  freedom  from  the  peril  of  fire.  The  relative 
expense  of  the  two  systems  is  determined  by  the  cost  of  materials 
and  labor.  Two  extreme  cases  illustrate  the  result  of  these 
economic  factors  with  sufficient  clearness.  It  is  stated  that  the 
cost  of  timbering  stopes  on  the  Le  Roi  Mine  by  square-sets  is 
about  21  cents  per  ton  of  ore  excavated.  In  the  Ivanhoe  mine 
of  West  Australia  the  cost  of  filling  stopes  with  tailings  is 
about  22  cents  per  ton  of  ore  excavated.  At  the  former  mine  the 
average  cost  of  timber  is  under  $10  per  M  board-measure,  while  at 
the  latter  its  price  would  be  $50  per  M  board-measure ;  although 
labor  is  about  of  the  same  efficiency  and  wage,  the  cost  in  the 
Ivanhoe  by  square-setting  would  be  about  65  cents  per  ton  of 
ore  broken.  In  the  Le  Roi,  on  the  other  hand,  no  residues  are 
available  for  filling.  To  quarry  rock  or  drive  crosscuts  into  the 
walls  might  make  this  system  cost  65  cents  per  ton  of  ore  broken 
if  applied  to  that  mine.  The  comparative  value  of  the  filling 
method  with  other  systems  will  be  discussed  later. 

Filling  with  Broken  Ore  subsequently  Withdrawn. — This 
order  of  support  is  called  by  various  names,  the  favorite  being 
"shrinkage-stoping."  The  method  is  to  break  the  ore  onto  the 
roof  of  the  level,  and  by  thus  filling  the  stope  with  broken  ore, 
provide  temporary  support  to  the  walls  and  furnish  standing 
floor  upon  which  to  work  in  making  the  next  cut  (Figs.  37,  38, 
and  39.)  As  broken  material  occupies  30  to  40%  more  space 
than  rock  in  situ,  in  order  to  provide  working  space  at  the  face, 
the  broken  ore  must  be  drawn  from  along  the  level  after  eadi  cut. 
When  the  area  attacked  is  completely  broken  through  from 
level  to  level,  the  stope  will  be  full  of  loose  broken  ore,  which  is 
then  entirely  drawn  off. 


METHODS  OF  SUPPORTING  EXCAVATION. 


113 


A  block  to  be  attacked  by  this  method  requires  preliminary 
winzes  only  at  the  extremities  of  the  stope, —  for  entry  and  for 
ventilation.  Where  it  is  desired  to  maintain  the  winzes  after 
stoping,  they  must  either  be  strongly  timbered  and  lagged  on 
the  stope  side,  be  driven  in  the  walls,  or  be  protected  by  a  pillar 
of  ore  (Fig.  37).  The  settling  ore  and  the  crushing  after  the 
stope  is  empty  make  it  difficult  to  maintain  timbered  winzes. 


FIG.  37.  —  Longitudinal  section  of  stope  filled  with  broken  ore. 

Where  it  can  be  done  without  danger  to  the  mine,  the  empty 
stopes  are  allowed  to  cave.  If  such  crushing  would  be  danger- 
ous, either  the  walls  must  be  held  up  by  pillars  of  unbroken  ore, 
as  in  the  Alaska  Treadwell,  where  large  "rib"  pillars  are  left, 
or  the  open  spaces  must  be  rilled  with  waste.  Filling  the  empty 
stope  is  usually  done  by  opening  frequent  passes  along  the  base 
of  the  filled  stope  above,  and  allowing  the  material  of  the  upper 
stope  to  flood  the  lower  one.  This  program  continued  upwards 
through  the  mine  allows  the  whole  filling  of  the  mine  to  descend 
gradually  and  thus  requires  replenishment  only  into  the  top. 
The  old  stopes  in  the  less  critical  and  usually  exhausted  terri- 
tory nearer  the  surface  are  sometimes  left  without  replenishing 
their  filling. 

The  weight  of  broken  ore  standing  at  such  a  high  angle  as  to 
settle  rapidly  is  very  considerable  upon  the  level;  moreover,  at 
the  moment  when  the  stope  is  entirely  drawn  off,  the  pressure 


114 


PRINCIPLES   OF  MINING. 


of  the  walls  as  well  is  likely  to  be  very  great.  The  roadways  in 
this  system  therefore  require  more  than  usual  protection.  Three 
methods  are  used:  (a)  timbering;  (b)  driving  a  sublevel  in  the 
ore  above  the  main  roadway  as  a  stoping-base,  thus  leaving  a 
pillar  of  ore  over  the  roadway  (Fig.  39) ;  (c)  by  dry-walling  the 
levels,  as  in  the  Baltic  mine,  Michigan  (Figs.  34  and  35).  By 


FIG.  38.  —  Cross-section  of  "  shrinkage  "  slope. 

the  use  of  sublevels  the  main  roadways  are  sometimes  driven 
in  the  walls  (Fig.  38)  and  in  many  cases  all  timbering  is  saved. 
To  recover  pillars  left  below  sublevels  is  a  rather  difficult  task, 
especially  if  the  old  stope  above  is  caved  or  filled.  The  use  of 
pillars  in  substitution  for  timber,  if  the  pillars  are  to  be  lost,  is 
simply  a  matter  of  economics  as  to  whether  the  lost  ore  would 
repay  the  cost  of  other  devices. 


METHODS  OF  SUPPORTING   EXCAVATION. 


115 


Frequent  ore-chutes  through  the  level  timbers,  or  from  the 
sublevels,  are  necessary  to  prevent  lodgment  of  broken  ore 
between  such  passes,  because  it  is  usually  too  dangerous  for  men 
to  enter  the  emptying  stope  to  shovel  out  the  lodged  remnants. 
Where  the  ore-body  is  wide,  and  in  order  that  there  may  be  no 


FIG.  39.  —  Cross-section  of  "shrinkage  "  stope. 

lodgment  of  ore,  the  timbers  over  the  level  are  set  so  as  to  form 
a  trough  along  the  level ;  or  where  pillars  are  left,  they  are  made 
"  A  "-shaped  between  the  chutes,  as  indicated  in  Figure  37. 

The  method  of  breaking  the  ore  in  conjunction  with  this 
means  of  support  in  comparatively  narrow  deposits  can  be  on 
the  rill,  in  order  to  have  the  advantage  of  down  holes.  Usually, 
however,  flat-back  or  horizontal  cuts  are  desirable,  as  in  such 


116  PRINCIPLES  OF  MINING. 

an  arrangement  it  is  less  troublesome  to  regulate  the  drawing  of 
the  ore  so  as  to  provide  proper  head  room.  Where  stopes  are 
wide,  ore  is  sometimes  cut  arch-shaped  from  wall  to  wall  to, 
assure  its  standing.  Where  this  method  of  support  is  not  of 
avail,  short,  sharply  tapering  stulls  are  put  in  from  the  broken 
ore  to  the  face  (Fig.  39).  When  the  cut  above  these  stulls  is 
taken  out,  they  are  pulled  up  and  are  used  again. 
This  method  of  stoping  is  only  applicable  when :  — 

1.  The  deposit  dips  over  60°,  and  thus  broken  material  will 
freely  settle  downward  to  be  drawn  off  from  the  bottom. 

2.  The  ore  is  consistently  payable  in  character.     No  selec- 
tion can  be  done  in  breaking,  as  all  material  broken  must  be 
drawn  off  together. 

3.  The  hanging  wall  is  strong,  and  will  not  crush  or  spall 
off  waste  into  the  ore. 

4.  The  ore-body  is  regular  in  size,  else  loose  ore  will  lodge 
on  the  foot  wall.     Stopes  opened  in  this  manner  when  partially 
empty  are  too  dangerous  for  men  to  enter  for  shoveling  out 
remnants. 

The  advantages  of  this  system  over  others,  where  it  is  ap- 
plicable, are:  — 

(a)  A  greater  distance  between  levels  can  be  operated  and 
few  winzes  and  rises  are  necessary,  thus  a  great  saving  of  develop- 
ment work  can  be  effected.  A  stope  800  to  1000  feet  long  can 
be  operated  with  a  winze  at  either  end  and  with  levels  200  or  220 
feet  apart. 

(&)  There  is  no  shoveling  in  the  stopes  at  all. 

(c)  No  timber  is  required.     As  compared  with  timbering 
by  stulling,  it  will  apply  to  stopes  too  wide  and  walls  too  heavy 
for  this  method.     Moreover,  little  staging  is  required  for  work- 
ing the  face,  since  ore  can  be  drawn  from  below  in  such  a  man- 
ner as  to  allow  just  the  right  head  room. 

(d)  Compared  to  the  system  of  filling  with  waste,  coinciden- 
tally  with  breaking  (second  method) ,  it  saves  altogether  in  some 
cases  the  cost  of  filling.     In  any  event,  it  saves  the  cost  of  ore- 
passes,  of  shoveling  into  them,  and  of  the  detailed  distribution 
of  the  filling. 


METHODS  OF  SUPPORTING   EXCAVATION.  117 

Compared  with  other  methods,  the  system  has  the  following 
disadvantages,  that :  — 

A.  The  ore  requires  to  be  broken  in  the  stopes  to  a  degree 
of  fineness  which  will  prevent  blocking  of  the  chutes  at  the 
level.     When  pieces  too  large  reach  the  chutes,  nothing  will 
open  them  but  blasting,  —  to  the  damage  of  timbers  and  chutes. 
Some  large  rocks  are  always  liable  to  be  buried  in  the  course  of 
ore-breaking. 

B.  Practically  no  such  perfection  of  walls  exists,  but  some 
spalling  of  waste  into  the  ore  will  take  place.     A  crushing  of  the 
walls  would  soon  mean  the  loss  of  large  amounts  of  ore. 

C.  There  is  no  possibility  of  regulating  the  mixture  of  grade 
of  ore  by  varying  the  working  points.     It  is  months  after  the  ore 
is  broken  before  it  can  reach  the  levels. 

D.  The  breaking  of  60%  more  ore  than  immediate  treatment 
demands  results  in  the  investment  of  a  considerable  sum  of  money. 
An  equilibrium  is  ultimately  established  in  a  mine  worked  on  this 
system  when  a  certain  number  of  stopes  full  of  completely  broken 
ore  are  available  for  entire  withdrawal,  and  there  is  no  further 
accumulation.     But,  in  any  event,  a  considerable  amount  of 
broken  ore  must  be  held  in  reserve.     In  one  mine  worked  on  this 
plan,  with  which  the  writer  has  had  experience,  the  annual  pro- 
duction is  about  250,000  tons  and  the  broken  ore  represents  an 
investment  which,  at  5%,  means  an  annual  loss  of  interest 
amounting  to  7  cents  per  ton  of  ore  treated. 

E.  A  mine  once  started  on  the  system  is  most  difficult  to 
alter,  owing  to  the  lack  of  frequent  winzes  or  passes.     Especially 
is  this  so  if  the  only  alternative  is  filling,  for  an  alteration  to  the 
system  of  filling  coincident  with  breaking  finds  the  mine  short 
of  filling  winzes.    As  the  conditions  of  walls  and  ore  often  alter 
with  depth,  change  of  system  may  be  necessary  and  the  situation 
may  become  very  embarrassing. 

F.  The  restoping  of  the  walls  for  lower-grade  ore  at  a  later 
period  is  impossible,  for  the  walls  of  the  stope  will  be  crushed, 
or,  if  filled  with  waste,  will  usually  crush  when  it  is  drawn  off 
to  send  to  a  lower  stope. 

The  system  has  much  to  recommend  it  where  conditions 


118 


PRINCIPLES  OF  MINING. 


are  favorable.  Like  all  other  alternative  methods  of  mining, 
it  requires  the  most  careful  study  in  the  light  of  the  special  con- 
ditions involved.  In  many  mines  it  can  be  used  for  some  stopes 
where  not  adaptable  generally.  It  often  solves  the  problem  of 
blind  ore-bodies,  for  they  can  by  this  means  be  frequently  worked 
with  an  opening  underneath  only.  Thus  the  cost  of  driving  a 
roadway  overhead  is  avoided,  which  would  be  required  if  timber 
or  coincident  filling  were  the  alternatives.  In  such  cases  ventila- 
tion can  be  managed  without  an  opening  above,  by  so  directing 
the  current  of  air  that  it  will  rise  through  a  winze  from  the 
level  below,  flow  along  the  stope  and  into  the  level  again  at  the 
further  end  of  the  stope  through  another  winze. 


L        E 


V          E 


FIG.  40.  —  Longitudinal  section.     Ore-pillar  support  in  narrow  stopes. 

Support  by  Pillars  of  Ore.  —  As  a  method  of  mining  metals 
of  the  sort  under  discussion,  the  use  of  ore-pillars  except  in 
conjunction  with  some  other  means  of  support  has  no  general 
application.  To  use  them  without  assistance  implies  walls 
sufficiently  strong  to  hold  between  pillars;  to  leave  them  per- 
manently anywhere  implies  that  the  ore  abandoned  would  not 
repay  the  labor  and  the  material  of  a  substitute.  There  are 
cases  of  large,  very  low-grade  mines  whereto  abandon  one-half 
the  ore  as  pillars  is  more  profitable  than  total  extraction,  but 
the  margin  of  payability  in  such  ore  must  be  very,  very  narrow. 
Unpayable  spots  are  always  left  as  pillars,  for  obvious  reasons. 


METHODS   OF  SUPPORTING   EXCAVATION. 


119 


Permanent  ore-pillars  as  an  adjunct  to  other  methods  of  support 
are  in  use.  Such  are  the  rib-pillars  in  the  Alaska  Treadwell,  the 
form  of  which  is  indicated  by  the  upward  extension  of  the 


FIG.  41.  —  Horizontal  plan  at  levels  of  Broken  Hill. 

and  ore-pillars. 


Method  of  alternate  stopes 


pillars  adjacent  to  the  winzes,  shown  in  Figure  37.  Always  a 
careful  balance  must  be  cast  as  to  the  value  of  the  ore  left,  and 
as  to  the  cost  of  a  substitute,  because  every  ore-pillar  can  be  re- 
moved at  some  outlay.  Temporary  pillars  are  not  unusual,  par- 
ticularly to  protect  roadways  and  shafts.  They  are,  when  left 
for  these  purposes,  removed  ultimately,  usually  by  beginning  at 
the  farther  end  and  working  back  to  the  final  exit. 


FIG.  42.  —  Longitudinal  section  of  Figure  41. 

A  form  of  temporary  ore-pillars  in  very  wide  deposits  is 
made  use  of  in  conjunction  with  both  filling  and  timbering 
(Figs,  37,  39,  40).  In  the  use  of  temporary  pillars  for  ore-bodies 


120 


PRINCIPLES   OF  MINING. 


100  to  250  feet  wide  at  Broken  Hill,  stopes  are  carried  up  at 
right  angles  to  the  strike,  each  fifty  feet  wide  and  clear  across  the 
ore-body  (Figs.  41  and  42).  A  solid  pillar  of  the  same  width 
is  left  in  the  first  instance  between  adjacent  stopes,  and  the 
initial  series  of  stopes  are  walled  with  one  square-set  on  the  sides 


FIG.  43.  —  Cross-section  of  stull  support  with  waste  reenforcement. 

as  the  stope  is  broken  upward.  The  room  between  these  two 
lines  of  sets  is  filled  with  waste  alternating  with  ore-breaking  in 
the  usual  filling  method.  When  the  ore  from  the  first  group  of 
alternate  stopes  (ABC,  Fig.  42)  is  completely  removed,  the  pillars 
are  stoped  out  and  replaced  with  waste.  The  square-sets 
of  the  first  set  of  stopes  thus  become  the  boundaries  of  the 
second  set.  Entry  and  ventilation  are  obtained  through  these 


METHODS  OF  SUPPORTING   EXCAVATION. 


121 


lines  of  square-sets,  and  the  ore  is  passed  out  of  the  stopes  through 
them. 

Artificial  Pillars.  —  This  system  also  implies  a  roof  so  strong  as 
not  to  demand  continuous  support.  Artificial  pillars  are  built  in 
many  different  ways.  The  method  most  current  in  fairly  narrow 
deposits  is  to  reenforce  stulls  by  packing  waste  above  them 
(Figs.  43  and  44).  Not  only  is  it  thus  possible  to  economize  in 
stulls  by  using  the  waste  which  accumulates  underground,  but 
the  principle  applies  also  to  cases  where  the  stulls  alone  are  not 
sufficient  support,  and  yet  where  complete  filling  or  square-setting 


FIG.  44.  —  Longitudinal  section  of  stull  and  waste  pillars. 

is  unnecessary.  When  the  conditions  are  propitious  for  this 
method,  it  has  the  comparative  advantage  over  timber  systems  of 
saving  timber,  and  over  filling  systems  of  saving  imported  filling. 
Moreover,  these  constructions  being  pillar-shaped  (Fig.  44), 
the  intervals  between  them  provide  outlets  for  broken  ore,  and 
specially  built  passes  are  unnecessary.  The  method  has  two 
disadvantages  as  against  the  square-set  or  filling  process,  in 
that  more  staging  must  be  provided  from  which  to  work,  and  in 
stopes  over  six  feet  the  erection  of  machine-drill  columns  is  tedious 
and  costly  in  time  and  wages. 

In  wide  deposits  of  markedly  flat,  irregular  ore-bodies,  where 
a  definite  system  is  difficult  and  where  timber  is  expensive,  cribs 
of  cord-wood  or  logs  filled  with  waste  after  the  order  shown  in 


122 


PRINCIPLES   OF  MINING. 


Figure  31,  often  make  fairly  sound  pillars.  They  will  not  last 
indefinitely  and  are  best  adapted  to  the  temporary  support  of  the 
ore-roof  pending  filling.  The  increased  difficulty  in  setting  up 
machine  drills  in  such  stopes  adds  to  the  breaking  costs,  —  often 
enough  to  warrant  another  method  of  support. 


MAIN  LEVEL 


MAIN  LEVEL 


FIG.  45.  —  Sublevel  caving  system. 

Caving  Systems.  —  This  method,  with  variations,  has  been 
applied  to  large  iron  deposits,  to  the  Kimberley  diamond  mines, 
to  some  copper  mines,  but  in  general  it  has  little  applica- 
tion to  the  metal  mines  under  consideration,  as  few  ore-bodies  are 
of  sufficiently  large  horizontal  area.  The  system  is  dependent 
upon  a  large  area  of  loose  or  " heavy"  ground  pressing  directly 
on  the  ore  with  weight,  such  that  if  the  ore  be  cut  into  pillars; 


METHODS  OF  SUPPORTING  EXCAVATION.  123 

these  will  crush.  The  details  of  the  system  vary,  but  in  general 
the  modus  operandi  is  to  prepare  roadways  through  the  ore,  and 
from  the  roadways  to  put  rises,  from  which  sublevels  are  driven 
close  under  the  floating  mass  of  waste  and  ore,  —  sometimes  called 
the  " matte"  (Fig.  45).  The  pillars  between  these  sublevels 
are  then  cut  away  until  the  weight  above  crushes  them  down. 
When  all  the  crushed  ore  which  can  be  safely  reached  is  extracted, 
retreat  is  made  and  another  series  of  subopenings  is  then  driven 
close  under  the ' '  matte. ' '  The  pillar  is  reduced  until  it  crushes  and 
the  operation  is  repeated.  Eventually  the  bottom  strata  of  the 
"matte"  become  largely  ore,  and  a  sort  of  equilibrium  is  reached 
when  there  is  not  much  loss  in  this  direction.  "Top  slicing"  is  a 
variation  of  the  above  method  by  carrying  a  horizontal  stope 
from  the  rises  immediately  under  the  matte,  supporting  the 
floating  material  with  timber.  At  Kimberley  the  system  is 
varied  in  that  galleries  are  run  out  to  the  edge  of  the  diamond- 
iferous  area  and  enlarged  until  the  pillar  between  crushes. 

In  the  caving  methods,  between  40  and  50%  of  the  ore  is  re- 
moved by  the  preliminary  openings,  and  as  they  are  all  headings  of 
some  sort,  the  average  cost  per  ton  of  this  particular  ore  is  higher 
than  by  ordinary  sloping  methods.  On  the  other  hand,  the 
remaining  50  to  60%  of  the  ore  costs  nothing  to  break,  and  the 
average  cost  is  often  remarkably  low.  As  said,  the  system  im- 
plies bodies  of  large  horizontal  area.  They  must  start  near  enough 
to  the  surface  that  the  whole  superincumbent  mass  may  cave 
and  give  crushing  weight,  or  the  immediately  overhanging  roof 
must  easily  cave.  All  of  these  are  conditions  not  often  met 
with  in  mines  of  the  character  under  review. 


CHAPTER  XII. 
MECHANICAL  EQUIPMENT. 

CONDITIONS  BEARING  ON  MINE  EQUIPMENT ;  WINDING  APPLIANCES ; 
HAULAGE  EQUIPMENT  IN  SHAFTS;  LATERAL  UNDERGROUND 
TRANSPORT;  TRANSPORT  IN  STOPES. 

THERE  is  no  type  of  mechanical  engineering  which  presents 
such  complexities  in  determination  of  the  best  equipment  as  does 
that  of  mining.  Not  only  does  the  economic  side  dominate  over 
pure  mechanics,  but  machines  must  be  installed  and  operated  under 
difficulties  which  arise  from  the  most  exceptional  and  conflicting 
conditions,  none  of  which  can  be  entirely  satisfied.  Compromise 
between  capital  outlay,  operating  efficiency,  and  conflicting 
demands  is  the  key-note  of  the  work. 

These  compromises  are  brought  about  by  influences  which 
lie  outside  the  questions  of  mechanics  of  individual  machines, 
and  are  mainly  as  follows :  — 

1.  Continuous  change  in  horizon  of  operations. 

2.  Uncertain  life  of  the  enterprise. 

3.  Care  and  preservation  of  human  life. 

4.  Unequal  adaptability  of  power  transmission  mediums. 

5.  Origin  of  power. 

First.  —  The  depth  to  be  served  and  the  volume  of  ore  and 
water  to  be  handled,  are  not  only  unknown  at  the  initial 
equipment,  but  they  are  bound  to  change  continuously  in  quan- 
tity, location,  and  horizon  with  the  extension  of  the  workings. 

Second.  —  From  the  mine  manager's  point  of  view,  which 
must  embrace  that  of  the  mechanical  engineer,  further  difficulty 
presents  itself  because  the  life  of  the  enterprise  is  usually  unknown, 
and  therefore  a  manifest  necessity  arises  for  an  economic  balance 
of  capital  outlay  and  of  operating  efficiency  commensurate  with 

124 


MECHANICAL  EQUIPMENT.  125 

the  prospects  of  the  mine.  Moreover,  the  initial  capital  is  often 
limited,  and  makeshifts  for  this  reason  alone  must  be  provided. 
In  net  result,  no  mineral  deposit  of  speculative  ultimate  volume 
of  ore  warrants  an  initial  equipment  of  the  sort  that  will  meet 
every  eventuality,  or  of  the  kind  that  will  give  even  the  maximum 
efficiency  which  a  free  choice  of  mining  machinery  could  obtain. 

Third.  —  In  the  design  and  selection  of  mining  machines,  the 
safety  of  human  life,  the  preservation  of  the  health  of  workmen 
under  conditions  of  limited  space  and  ventilation,  together  with 
reliability  and  convenience  in  installing  and  working  large 
mechanical  tools,  all  dominate  mechanical  efficiency.  For 
example,  compressed-air  transmission  of  power  best  meets  the 
requirements  of  drilling,  yet  the  mechanical  losses  in  the  genera- 
tion, the  transmission,  and  the  application  of  compressed  air 
probably  total,  from  first  to  last,  70  to  85%. 

Fourth.  —  All  machines,  except  those  for  shaft  haulage, 
must  be  operated  by  power  transmitted  from  the  surface, 
as  obviously  power  generation  underground  is  impossible. 
The  conversion  of  power  into  a  transmission  medium  and 
its  transmission  are,  at  the  outset,  bound  to  be  the  occasions 
of  loss.  Not  only  are  the  various  forms  of  transmission  by 
steam,  electricity,  compressed  air,  or  rods,  of  different  effi- 
ciency, but  no  one  system  lends  itself  to  universal  or  economi- 
cal application  to  all  kinds  of  mining  machines.  Therefore 
it  is  not  uncommon  to  find  three  or  four  different  media  of 
power  transmission  employed  on  the  same  mine.  To  illus- 
trate: from  the  point  of  view  of  safety,  reliability,  control, 
and  in  most  cases  economy  as  well,  we  may  say  that  direct 
steam  is  the  best  motive  force  for  winding-engines;  that  for 
mechanical  efficiency  and  reliability,  rods  constitute  the  best 
media  of  power  transmission  to  pumps;  that,  considering  venti- 
lation and  convenience,  compressed  air  affords  the  best  medium 
for  drills.  Yet  there  are  other  conditions  as  to  character  of 
the  work,  volume  of  water  or  ore,  and  the  origin  of  power 
which  must  in  special  instances  modify  each  and  every  one  of 
these  generalizations.  For  example,  although  pumping  water 
with  compressed  air  is  mechanically  the  most  inefficient  of 


126  PRINCIPLES  OF  MINING. 

devices,  it  often  becomes  the  most  advantageous,  because 
compressed  air  may  be  of  necessity  laid  on  for  other  purposes, 
and  the  extra  power  required  to  operate  a  small  pump  may 
be  thus  most  cheaply  provided. 

Fifth.  —  Further  limitations  and  modifications  arise  out 
of  the  origin  of  power,  for  the  sources  of  power  have  an  intimate 
bearing  on  the  type  of  machine  and  media  of  transmission. 
This  very  circumstance  often  compels  giving  away  efficiency 
and  convenience  in  some  machines  to  gain  more  in  others. 
This  is  evident  enough  if  the  principal  origins  of  power  genera- 
tion be  examined.  They  are  in  the  main  as  follows:  — 

a.  Water-power  available  at  the  mine. 

b.  Water-power  available   at  a  less  distance  than  three 

or  four  miles. 

c.  Water-power  available  some  miles  away,  thus  necessi- 

tating electrical  transmission  (or  purchased  electrical 
power). 

d.  Steam-power  to  be  generated  at  the  mine. 

e.  Gas-power  to  be  generated  at  the  mine. 

a.  With  water-power  at  the  mine,  winding  engines  can  be 
operated  by  direct  hydraulic  application  with  a  gain  in  economy 
over  direct  steam,  although  with  the  sacrifice  of  control  and 
reliability.  Rods  for  pumps  can  be  driven  directly  with 
water,  but  this  superiority  in  working  economy  means,  as 
discussed  later,  a  loss  of  flexibility  and  increased  total  outlay 
over  other  forms  of  transmission  to  pumps.  As  compressed 
air  must  be  transmitted  for  drills,  the  compressor  would  be 
operated  direct  from  water-wheels,  but  with  less  control  in 
regularity  of  pressure  delivery. 

6.  With  water-power  a  short  distance  from  the  mine,  it 
would  normally  be  transmitted  either  by  compressed  air  or  by 
electricity.  Compressed-air  transmission  would  better  satisfy 
winding  and  drilling  requirements,  but  would  show  a  great 
comparative  loss  in  efficiency  over  electricity  when  applied 
to  pumping.  Despite  the  latter  drawback,  air  transmission 
is  a  method  growing  in  favor,  especially  in  view  of  the  advance 
made  in  effecting  compression  by  falling  water. 


MECHANICAL  EQUIPMENT.  127 

c.  In   the   situation   of    transmission    too    far    for    using 
compressed  air,  there  is  no  alternative  but  electricity.     In 
these  cases,  direct  electric  winding  is  done,  but  under  such 
disadvantages  that  it  requires  a  comparatively  very  cheap 
power  to    take   precedence   over  a    subsidiary   steam   plant 
for   this  purpose.     Electric  air-compressors  work  under  the 
material  disadvantage  of  constant  speed  on  a  variable  load, 
but  this  installation  is  also  a  question  of  economics.     The 
pumping  service  is  well  performed  by  direct  electrical  pumps. 

d.  In    this    instance,  winding    and    air-compression    are 
well  accomplished  by  direct  steam  applications;    but  pump- 
ing   is  beset    with    wholly  undesirable    alternatives,  among 
which  it  is  difficult  to  choose. 

e.  With    internal   combustion    engines,   gasoline    (petrol) 
motors  have  more  of  a  position  in  experimental  than  in  sys- 
tematic mining,  for  their  application  to  winding  and  pumping 
and  drilling  is  fraught  with  many  losses.     The  engine  must  be 
under  constant  motion,  and  that,  too,  with  variable  loads. 
Where  power  from  producer  gas  is  used,  there  is  a  greater 
possibility  of  installing  large  equipments,  and  it  is  generally 
applied  to   the  winding  and  lesser  units   by  conversion  into 
compressed  air  or  electricity  as  an  intermediate  stage. 

One  thing  becomes  certain  from  these  examples  cited,  that 
the  right  installation  for  any  particular  portion  of  the  mine's 
equipment  cannot  be  determined  without  reference  to  all  the 
others.  The  whole  system  of  power  generation  for  surface 
work,  as  well  as  the  transmission  underground,  must  be 
formulated  with  regard  to  furnishing  the  best  total  result 
from  all  the  complicated  primary  and  secondary  motors,  even 
at  the  sacrifice  of  some  members. 

Each  mine  is  a  unique  problem,  and  while  it  would  be 
easy  to  sketch  an  ideal  plant,  there  is  no  mine  within  the 
writer's  knowledge  upon  which  the  ideal  would,  under  the 
many  variable  conditions,  be  the  most  economical  of  instal- 
lation or  the  most  efficient  of  operation.  The  dominant 
feature  of  the  task  is  an  endeavor  to  find  a  compromise  between 
efficiency  and  capital  outlay.  The  result  is  a  series  of  choices 


128  PRINCIPLES  OF  MINING. 

between  unsatisfying  alternatives,  a  number  of  which  are 
usually  found  to  have  been  wrong  upon  further  extension 
of  the  mine  in  depth. 

In  a  general  way,  it  may  be  stated  that  where  power  is 
generated  on  the  mine,  economy  in  labor  of  handling  fuel, 
driving  engines,  generation  and  condensing  steam  where  steam 
is  used,  demand  a  consolidated  power  plant  for  the  whole 
mine  equipment.  The  principal  motors  should  be  driven 
direct  by  steam  or  gas,  with  power  distribution  by  electricity 
to  all  outlying  surface  motors  and  sometimes  to  underground 
motors,  and  also  to  some  underground  motors  by  compressed 
air. 

Much  progress  has  been  made  in  the  past  few  years  in 
the  perfection  of  larger  mining  tools.  Inherently  many  of  our 
devices  are  of  a  wasteful  character,  not  only  on  account  of 
the  need  of  special  forms  of  transmission,  but  because  they 
are  required  to  operate  under  greatly  varying  loads.  As  an 
outcome  of  transmission  losses  and  of  providing  capacity  to 
cope  with  heavy  peak  loads,  their  efficiency  on  the  basis  of 
actual  foot-pounds  of  work  accomplished  is  very  low. 

The  adoption  of  electric  transmission  in  mine  work,  while 
in  certain  phases  beneficial,  has  not  decreased  the  perplexity 
which  arises  from  many  added  alternatives,  none  of  which 
are  as  yet  a  complete  or  desirable  answer  to  any  mine  problem. 
When  a  satisfactory  electric  drill  is  invented,  and  a  method 
is  evolved  of  applying  electricity  to  winding-engines  that  will 
not  involve  such  abnormal  losses  due  to  high  peak  load 
then  we  will  have  a  solution  to  our  most  difficult  mechan- 
ical problems,  and  electricity  will  deserve  the  universal 
blessing  which  it  has  received  in  other  branches  of  mechanical 
engineering. 

It  is  not  intended  to  discuss  mine  equipment  problems 
from  the  machinery  standpoint,  —  there  are  thousands  of  dif- 
ferent devices,  —  but  from  the  point  of  view  of  the  mine 
administrator  who  finds  in  the  manufactory  the  various 
machines  which  are  applicable,  and  whose  work  then  becomes 
that  of  choosing,  arranging,  and  operating  these  tools. 


MECHANICAL  EQUIPMENT.  129 

The  principal  mechanical  questions  of  a  mine  may  be 
examined  under  the  following  heads:— 

1.  Shaft  haulage. 

2.  Lateral  underground  transport. 

3.  Drainage. 

4.  Rock  drilling. 

5.  Workshops. 

6.  Improvements  in  equipment. 

SHAFT   HAULAGE. 

Winding  Appliances.  —  No  device  has  yet  been  found  to 
displace  the  single  load  pulled  up  the  shaft  by  winding  a  rope 
on  a  drum.  Of  driving  mechanisms  for  drum  motors  the 
alternatives  are  the  steam-engine,  the  electrical  motor,  and 
infrequently  water-power  or  gas  engines. 

All  these  have  to  cope  with  one  condition  which,  on  the 
basis  of  work  accomplished,  gives  them  a  very  low  mechanical 
efficiency.  This  difficulty  is  that  the  load  is  intermittent, 
and  it  must  be  started  and  accelerated  at  the  point  of  maximum 
weight,  and  from  that  moment  the  power  required  diminishes 
to  less  than  nothing  at  the  end  of  the  haul.  A  large  number 
of  devices  are  in  use  to  equalize  partially  the  inequalities  of 
the  load  at  different  stages  of  the  lift.  The  main  lines  of 
progress  in  this  direction  have  been:  — 

a.  The  handling  of  two  cages  or  skips  with  one  engine 
or  motor,  the  descending  skip  partially  balancing 
the  ascending  one. 

6.  The  use  of  tail-ropes  or  balance  weights  to  compen- 
sate the  increasing  weight  of  the  descending  rope. 

c.  The  use  of  skips  instead  of  cages,  thus  permitting  of 

a  greater  percentage  of  paying  load. 

d.  The  direct  coupling  of  the  motor  to  the  drum  shaft. 

e.  The  cone-shaped  construction  of  drums,  —  this  latter 

being  now  largely  displaced  by  the  use  of  the  tail-rope. 

The  first  and  third  of  these  are  absolutely  essential  for 
anything  like  economy  and  speed;  the  others  are  refine- 


130  PRINCIPLES  OF  MINING. 

ments  depending  on  the  work  to  be  accomplished   and  the 
capital  available. 

Steam  winding-engines  require  large  cylinders  to  start 
the  load,  but  when  once  started  the  requisite  power  is  much 
reduced  and  the  load  is  too  small  for  steam  economy.  The 
throttling  of  the  engine  for  controlling  speed  and  reversing 
the  engine  at  periodic  stoppages  militates  against  the  maximum 
expansion  and  condensation  of  the  steam  and  further  increases 
the  steam  consumption.  In  result,  the  best  of  direct  com- 
pound condensing  engines  consume  from  60  to  100  pounds 
of  steam  per  horse-power  hour,  against  a  possible  efficiency 
of  such  an  engine  working  under  constant  load  of  less  than 
16  pounds  of  steam  per  horse-power  hour. 

It  is  only  within  very  recent  years  that  electrical  motors 
have  been  applied  to  winding.  Even  yet,  all  things  considered, 
this  application  is  of  doubtful  value  except  in  localities  of 
extremely  cheap  electrical  power.  The  constant  speed  of 
alternating  current  motors  at  once  places  them  at  a  disad- 
vantage for  this  work  of  high  peak  and  intermittent  loads. 
While  continuous-current  motors  can  be  made  to  partially 
overcome  this  drawback,  such  a  current,  where  power  is  pur- 
chased or  transmitted  a  long  distance,  is  available  only  by 
conversion,  which  further  increases  the  losses.  However, 
schemes  of  electrical  winding  are  in  course  of  development 
which  bid  fair,  by  a  sort  of  storage  of  power  in  heavy  fly-wheels 
or  storage  batteries  after  the  peak  load,  to  reduce  the  total 
power  consumption;  but  the  very  high  first  cost  so  far  prevents 
their  very  general  adoption  for  metal  mining. 

Winding-engines  driven  by  direct  water-  or  gas-power  are 
of  too  rare  application  to  warrant  much  discussion.  Gasoline 
driven  hoists  have  a  distinct  place  in  prospecting  and  early- 
stage  mining,  especially  in  desert  countries  where  transport 
and  fuel  conditions  are  onerous,  for  both  the  machines  and 
their  fuel  are  easy  of  transport.  As  direct  gas-engines  entail 
constant  motion  of  the  engine  at  the  power  demand  of  the 
peak  load,  they  are  hopeless  in  mechanical  efficiency. 

Like  all  other  motors  in  mining,  the  size  and  arrangement 


MECHANICAL  EQUIPMENT.  131 

of  the  motor  and  drum  are  dependent  upon  the  duty  which 
they  will  be  called  upon  to  perform.  This  is  primarily  depen- 
dent upon  the  depth  to  be  hoisted  from,  the  volume  of  the 
ore,  and  the  size  of  the  load.  For  shallow  depths  and  tonnages 
up  to,  say,  200  tons  daily,  geared  engines  have  a  place  on 
account  of  their  low  capital  cost.  Where  great  rope  speed 
is  not  essential  they  are  fully  as  economical  as  direct-coupled 
engines.  With  great  depths  and  greater  capacities,  speed 
becomes  a  momentous  factor,  and  direct-coupled  engines  are 
necessary.  Where  the  depth  exceeds  3,000  feet,  another 
element  enters  which  has  given  rise  to  much  debate  and  experi- 
ment; that  is,  the  great  increase  of  starting  load  due  to  the 
increased  length  and  size  of  ropes  and  the  drum  space  required 
to  hold  it.  So  far  the  most  advantageous  device  seems  to 
be  the  Whiting  hoist,  a  combination  of  double  drums  and 
tail  rope. 

On  mines  worked  from  near  the  surface,  where  depth  is 
gained  by  the  gradual  exhaustion  of  the  ore,  the  only  prudent 
course  is  to  put  in  a  new  hoist  periodically,  when  the  demand 
for  increased  winding  speed  and  power  warrants.  The  lack 
of  economy  in  winding  machines  is  greatly  augmented  if  they 
are  much  over-sized  for  the  duty.  An  engine  installed  to 
handle  a  given  tonnage  to  a  depth  of  3,000  feet  will  have  oper- 
ated with  more  loss  during  the  years  the  mine  is  pro- 
gressing from  the  surface  to  that  depth  than  several  inter- 
mediate-sized engines  would  have  cost.  On  most  mines  the 
uncertainty  of  extension  in  depth  would  hardly  warrant  such 
a  preliminary  equipment.  More  mines  are  equipped  with 
over-sized  than  with  under-sized  engines.  For  shafts  on  going 
metal  mines  where  the  future  is  speculative,  an  engine  will 
suffice  whose  size  provides  for  an  extension  in  depth  of  1,000 
feet  beyond  that  reached  at  the  time  of  its  installation.  The 
cost  of  the  engine  will  depend  more  largely  upon  the  winding 
speed  desired  than  upon  any  other  one  factor.  The  proper 
speed  to  be  arranged  is  obviously  dependent  upon  the  depth 
of  the  haulage,  for  it  is  useless  to  have  an  engine  able  to  wind 
3; 000  feet  a  minute  on  a  shaft  500  feet  deep,  since  it  could  never 


132  PRINCIPLES  OF  MINING. 

even  get  under  way ;  and  besides,  the  relative  operating  loss, 
as  said,  would  be  enormous. 

Haulage  Equipment  in  the  Shaft.  —  Originally,  material  was 
hoisted  through  shafts  in  buckets.  Then  came  the  cage  for 
transporting  mine  cars,  and  in  more  recent  years  the  "skip" 
has  been  developed.  The  aggrandized  bucket  or  "kibble"  of 
the  Cornishman  has  practically  disappeared,  but  the  cage  still 
remains  in  many  mines.  The  advantages  of  the  skip  over  the 
cage  are  many.  Some  of  them  are :  — 

a.  It  permits  25  to  40%  greater  load  of  material  in  propor- 

tion to  the  dead  weight  of  the  vehicle. 

b.  The  load  can  be  confined  within  a  smaller  horizontal 

space,  thus  the  area  of  the  shaft  need  not  be  so  great 
for  large  tonnages. 

c.  Loading  and  discharging  are  more  rapid,  and  the  latter 

is  automatic,  thus  permitting  more  trips  per  hour  and 
requiring  less  labor. 

d.  Skips  must  be  loaded  from  bins  underground,  and  by 

providing  in  the  bins  storage  capacity,  shaft  haulage  is 
rendered  independent  of  the  lateral  transport  in  the 
mine,  and  there  are  no  delays  to  the  engine  awaiting 
loads.  The  result  is  that  ore-winding  can  be  concen- 
trated into  fewer  hours,  and  indirect  economies  in  labor 
and  power  are  thus  effected. 

e.  Skips  save  the  time  of  the  men  engaged  in  the  lateral  haul- 

age, as  they  have  no  delay  waiting  for  the  winding  engine. 

Loads  equivalent  to  those  from  skips  are  obtained  in  some 
mines  by  double-decked  cages;  but,  aside  from  waste  weight 
of  the  cage,  this  arrangement  necessitates  either  stopping  the 
engine  to  load  the  lower  deck,  or  a  double-deck  loading  station. 
Double-deck  loading  stations  are  as  costly  to  install  and  more 
expensive  to  work  than  skip-loading  station  ore-bins.  Cages  are 
also  constructed  large  enough  to  take  as  many  as  four  trucks  on 
one  deck.  This  entails  a  shaft  compartment  double  the  size 
required  for  skips  of  the  same  capacity,  and  thus  enormously 
increases  shaft  cost  without  gaining  anything. 


MECHANICAL  EQUIPMENT.  133 

Altogether  the  advantages  of  the  skip  are  so  certain  and  so 
important  that  it  is  difficult  to  see  the  justification  for  the  cage 
under  but  a  few  conditions.  These  conditions  are  those  which 
surround  mines  of  small  output  where  rapidity  of  haulage  is  no 
object,  where  the  cost  of  station-bins  can  thus  be  evaded,  and  the 
convenience  of  the  cage  for  the  men  can  still  be  preserved.  The 
easy  change  of  the  skip  to  the  cage  for  hauling  men  removes  the 
last  objection  on  larger  mines.  There  occurs  also  the  situation 
in  which  ore  is  broken  under  contract  at  so  much  per  truck,  and 
where  it  is  desirable  to  inspect  the  contents  of  the  truck  when 
discharging  it,  but  even  this  objection  to  the  skip  can  be  ob- 
viated by  contracting  on  a  cubic-foot  basis. 

Skips  are  constructed  to  carry  loads  of  from  two  to  seven 
tons,  the  general  tendency  being  toward  larger  loads  every  year. 
One  of  the  most  feasible  lines  of  improvement  in  winding  is  in  the 
direction  of  larger  loads  and  less  speed,  for  in  this  way  the  sum 
total  of  dead  weight  of  the  vehicle  and  rope  to  the  tonnage  of 
ore  hauled  will  be  decreased,  and  the  efficiency  of  the  engine  will 
be  increased  by  a  less  high  peak  demand,  because  of  this  less 
proportion  of  dead  weight  and  the  less  need  of  high  acceleration. 


LATERAL  UNDERGROUND   TRANSPORT. 

Inasmuch  as  the  majority  of  metal  mines  dip  at  considerable 
angles,  the  useful  life  of  a  roadway  in  a  metal  mine  is  very  short 
because  particular  horizons  of  ore  are  soon  exhausted.  Therefore 
any  method  of  transport  has  to  be  calculated  upon  a  very  quick 
redemption  of  the  capital  laid  out.  Furthermore,  a  roadway  is 
limited  in  its  daily  traffic  to  the  product  of  the  stopes  which  it 
serves. 

Men  and  Animals.  —  Some  means  of  transport  must  be  pro- 
vided, and  the  basic  equipment  is  light  tracks  with  push-cars,  in 
capacity  from  half  a  ton  to  a  ton.  The  latter  load  is,  however, 
too  heavy  to  be  pushed  by  one  man.  As  but  one  car  can  be 
pushed  at  a  time,  hand-trucking  is  both  slow  and  expensive.  At 
average  American  or  Australian  wages,  the  cost  works  out 


134  PRINCIPLES  OF  MINING. 

between  25  and  35  cents  a  ton  per  mile.  An  improvement  of 
growing  import  where  hand-trucking  is  necessary  is  the  overhead 
mono-rail  instead  of  the  track. 

If  the  supply  to  any  particular  roadway  is  such  as  to  fully 
employ  horses  or  mules,  the  number  of  cars  per  trip  can  be  in- 
creased up  to  seven  or  eight.  In  this  case  the  expense,  including 
wages  of  the  men  and  wear,  tear,  and  care  of  mules,  will  work 
out  roughly  at  from  7  to  10  cents  per  ton  mile.  Manifestly,  if 
the  ore-supply  to  a  particular  roadway  is  insufficient  to  keep  a 
mule  busy,  the  economy  soon  runs  off. 

Mechanical  Haulage.  —  Mechanical  haulage  is  seldom  appli- 
cable to  metal  mines,  for  most  metal  deposits  dip  at  considerable 
angles,  and  therefore,  unlike  most  coal-mines,  the  horizon  of 
haulage  must  frequently  change,  and  there  are  no  main  arteries 
along  which  haulage  continues  through  the  life  of  the  mine. 
Any  mechanical  system  entails  a  good  deal  of  expense  for  instal- 
lation, and  the  useful  life  of  any  particular  roadway,  as  above 
said,  is  very  short.  Moreover,  the  crooked  roadways  of  most 
metal  mines  present  difficulties  of  negotiation  not  to  be  over- 
looked. In  order  to  use  such  systems  it  is  necessary  to  condense 
the  haulage  to  as  few  roadways  as  possible.  Where  the  tonnage 
on  one  level  is  not  sufficient  to  warrant  other  than  men  or  ani- 
mals, it  sometimes  pays  (if  the  dip  is-  steep  enough)  to  dump 
everything  through  winzes  from  one  to  two  levels  to  a  main  road 
below  where  mechanical  equipment  can  be  advantageously  pro- 
vided. The  cost  of  shaft- winding  the  extra  depth  is  inconsider- 
able compared  to  other  factors,  for  the  extra  vertical  distance  of 
haulage  can  be  done  at  a  cost  of  one  or  two  cents  per  ton  mile. 
Moreover,  from  such  an  arrangement  follows  the  concentration 
of  shaft-bins,  and  of  shaft  labor,  and  winding  is  accomplished 
without  so  much  shifting  as  to  horizon,  all  of  which  economies 
equalize  the  extra  distance  of  the  lift. 

There  are  three  principal  methods  of  mechanical  transport 
in  use:  — 

1.  Cable- ways. 

2.  Compressed-air  locomotives. 

3.  Electrical  haulage. 


MECHANICAL  EQUIPMENT.  135 

Cable-ways  or  endless  ropes  are  expensive  to  install;  and  to 
work  to  the  best  advantage  require  double  tracks  and  fairly 
straight  roads.  While  they  are  economical  in  operation  and 
work  with  little  danger  to  operatives,  the  limitations  mentioned 
preclude  them  from  adoption  in  metal  mines,  except  in  very 
special  circumstances  such  as  main  crosscuts  or  adit  tunnels, 
where  the  haulage  is  straight  and  concentrated  from  many 
sources  of  supply. 

Compressed-air  locomotives  are  somewhat  heavy  and  cum- 
bersome, and  therefore  require  well-built  tracks  with  heavy 
rails,  but  they  have  very  great  advantages  for  metal  mine  work. 
They  need  but  a  single  track  and  are  of  low  initial  cost  where 
compressed  air  is  already  a  requirement  of  the  mine.  No  sub- 
sidiary line  equipment  is  needed,  and  thus  they  are  free  to 
traverse  any  road  in  the  mine  and  can  be  readily  shifted  from 
one  level  to  another.  Their  mechanical  efficiency  is  not  so  low  in 
the  long  run  as  might  appear  from  the  low  efficiency  of  pneu- 
matic machines  generally,  for  by  storage  of  compressed  air  at 
the  charging  station  a  more  even  rate  of  energy  consumption  is 
possible  than  in  the  constant  cable  and  electrical  power  supply 
which  must  be  equal  to  the  maximum  demand,  while  the  air- 
plant  consumes  but  the  average  demand. 

Electrical  haulage  has  the  advantage  of  a  much  more  com- 
pact locomotive  and  the  drawback  of  more  expensive  track 
equipment,  due  to  the  necessity  of  transmission  wire,  etc.  It 
has  the  further  disadvantages  of  uselessness  outside  the  equipped 
haulage  way  and  of  the  dangers  of  the  live  wire  in  low  and  often 
wet  tunnels. 

In  general,  compressed-air  locomotives  possess  many  attrac- 
tions for  metal  mine  work,  where  air  is  in  use  in  any  event  and 
where  any  mechanical  system  is  at  all  justified.  Any  of  the 
mechanical  systems  where  tonnage  is  sufficient  in  quantity  to 
justify  their  employment  will  handle  material  for  from  1.5  to  4 
cents  per  ton  mile. 

Tracks.  —  Tracks  for  hand,  mule,  or  rope  haulage  are  usually 
built  with  from  12-  to  16-pound  rails,  but  when  compressed-air 
or  electrical  locomotives  are  to  be  used,  less  than  24-pound  rails 


136  PRINCIPLES  OF  MINING. 

are  impossible.  As  to  tracks  in  general,  it  may  be  said  that 
careful  laying  out  with  even  grades  and  gentle  curves  repays 
itself  many  times  over  in  their  subsequent  operation.  Further 
care  in  repair  and  lubrication  of  cars  will  often  make  a  difference 
of  75%  in  the  track  resistance. 

Transport  in  Stopes.  —  Owing  to  the  even  shorter  life  of  in- 
dividual stopes  than  levels,  the  actual  transport  of  ore  or  waste 
in  them  is  often  a  function  of  the  aboriginal  shovel  plus  gravity. 
As  shoveling  is  the  most  costly  system  of  transport  known,  any 
means  of  stoping  that  decreases  the  need  for  it  has  merit.  Shrink- 
age-stoping  eliminates  it  altogether.  In  the  other  methods, 
gravity  helps  in  proportion  to  the  steepness  of  the  dip.  When 
the  underlie  becomes  too  flat  for  the  ore  to  "run,"  transport  can 
sometimes  be  helped  by  pitching  the  ore-passes  at  a  steeper 
angle  than  the  dip  (Fig.  36).  In  some  cases  of  flat  deposits, 
crosscuts  into  the  walls,  or  even  levels  under  the  ore-body,  are 
justifiable.  The  more  numerous  the  ore-passes,  the  less  the  lat- 
eral shoveling,  but  as  passes  cost  money  for  construction  and 
for  repair,  there  is  a  nice  economic  balance  in  their  frequency. 

Mechanical  haulage  in  stopes  has  been  tried  and  finds  a  field 
under  some  conditions.  In  dips  under  25°  and  possessing  fairly 
sound  hanging-wall,  where  long-wall  or  flat-back  cuts  are  em- 
ployed, temporary  tracks  can  often  be  laid  in  the  stopes  and  the 
ore  run  in  cars  to  the  main  passes.  In  such  cases,  the  tracks  are 
pushed  up  close  to  the  face  after  each  cut.  Further  self-acting 
inclines  to  lower  cars  to  the  levels  can  sometimes  be  installed 
to  advantage.  This  arrangement  also  permits  greater  intervals 
between  levels  and  less  number  of  ore-passes.  For  dips  between 
25°  and  50°  where  the  mine  is  worked  without  stope  support  or 
with  occasional  pillars,  a  very  useful  contrivance  is  the  sheet- 
iron  trough  —  about  eighteen  inches  wide  and  six  inches  deep 
—  made  in  sections  ten  or  twelve  feet  long  and  readily  bolted 
together.  In  dips  35°  to  50°  this  trough,  laid  on  the  foot-wall, 
gives  a  sufficiently  smooth  surface  for  the  ore  to  run  upon. 
When  the  dip  is  flat,  the  trough,  if  hung  from  plugs  in  the 
hanging- wall,  may  be  swung  backward  and  forward.  The  use 
of  this  "  bumping-trougb  "  sa,ves  much  shoveling.  For  handling 


MECHANICAL  EQUIPMENT.  137 

filling  or  ore  in  flat  runs  it  deserves  wider  adoption.  It  is, 
of  course,  inapplicable  in  passes  as  a  "bumping-trough,"  but 
can  be  fixed  to  give  smooth  surface.  In  flat  mines  it  permits  a 
wider  interval  between  levels  and  therefore  saves  development 
work.  The  life  of  this  contrivance  is  short  when  used  in  open 
stopes,  owing  to  the  dangers  of  bombardment  from  blasting. 

In  dips  steeper  than  50°  much  of  the  shoveling  into  passes 
can  be  saved  by  rill-st oping,  as  described  on  page  100.  Where 
flat-backed  stopes  are  used  in  wide  ore-bodies  with  filling,  tem- 
porary tracks  laid  on  the  filling  to  the  ore-passes  are  useful,  for 
they  permit  wider  intervals  between  passes. 

In  that  underground  engineer's  paradise,  the  Witwatersrand, 
where  the  stopes  require  neither  timber  nor  filling,  the  long, 
moderately  pitched  openings  lend  themselves  particularly  to  the 
swinging  iron  troughs,  and  even  endless  wire  ropes  have  been 
found  advantageous  in  certain  cases. 

Where  the  roof  is  heavy  and  close  support  is  required,  and 
where  the  deposits  are  very  irregular  in  shape  and  dip,  there  is 
little  hope  of  mechanical  assistance  in  stope  transport. 


CHAPTER  XIII. 
MECHANICAL  EQUIPMENT  (Continued). 

DRAINAGE:     CONTROLLING   FACTORS;    VOLUME    AND    HEAD    OF 
WATER;    FLEXIBILITY;    RELIABILITY;    POWER    CONDITIONS; 

MECHANICAL  EFFICIENCY;  CAPITAL  OUTLAY.  SYSTEMS  OF 
DRAINAGE,  —  STEAM  PUMPS,  COMPRESSED-AIR  PUMPS,  ELEC- 
TRICAL PUMPS,  ROD-DRIVEN  PUMPS,  BAILING;  COMPARATIVE 
VALUE  OF  VARIOUS  SYSTEMS. 

WITH  the  exception  of  drainage  tunnels  —  more  fully  de- 
scribed in  Chapter  VIII  —  all  drainage  must  be  mechanical.  As 
the  bulk  of  mine  water  usually  lies  near  the  surface,  saving  in 
pumping  can  sometimes  be  effected  by  leaving  a  complete  pillar 
of  ore  under  some  of  the  upper  levels.  In  many  deposits,  how- 
ever, the  ore  has  too  many  channels  to  render  this  of  much  avail. 

There  are  six  factors  which  enter  into  a  determination  of 
mechanical  drainage  systems  for  metal  mines :  — 

1.  Volume  and  head  of  water. 

2.  Flexibility  to  fluctuation  in  volume  and  head. 

3.  Reliability. 

4.  Capital  cost. 

5.  The  general  power  conditions. 

6.  Mechanical  efficiency. 

In  the  drainage  appliances,  more  than  in  any  other  feature  of 
the  equipment,  must  mechanical  efficiency  be  subordinated  to 
the  other  issues. 

Flexibility.  —  Flexibility  in  plant  is  necessary  because  vol- 
ume and  head  of  water  are  fluctuating  factors.  In  wet  regions 
the  volume  of  water  usually  increases  for  a  certain  distance  with 
the  extension  of  openings  in  depth.  In  dry  climates  it  gener- 
ally decreases  with  the  downward  extension  of  the  workings 

138 


MECHANICAL  EQUIPMENT.  139 

after  a  certain  depth.  Moreover,  as  depth  progresses,  the  water 
follows  the  openings  more  or  less  and  must  be  pumped  against 
an  ever  greater  head.  In  most  cases  the  volume  varies  with 
the  seasons.  What  increase  will  occur,  from  what  horizon  it 
must  be  lifted,  and  what  the  fluctuations  in  volume  are  likely 
to  be,  are  all  unknown  at  the  time  of  installation.  If  a  pump- 
ing system  were  to  be  laid  out  for  a  new  mine,  which  would 
peradventure  meet  every  possible  contingency,  the  capital  outlay 
would  be  enormous,  and  the  operating  efficiency  would  be  very 
low  during  the  long  period  in  which  it  would  be  working  below 
its  capacity.  The  question  of  flexibility  does  not  arise  so  promi- 
nently in  coal-mines,  for  the  more  or  less  flat  deposits  give  a 
fixed  factor  of  depth.  The  flow  is  also  more  steady,  and  the  vol- 
ume can  be  in  a  measure  approximated  from  general  experience. 

Reliability.  —  The  factor  of  reliability  was  at  one  time  of 
more  importance  than  in  these  days  of  high-class  manufacture 
of  many  different  pumping  systems.  Practically  speaking,  the 
only  insurance  from  flooding  in  any  event  lies  in  the  provision 
of  a  relief  system  of  some  sort,  —  duplicate  pumps,  or  the  sim- 
plest and  most  usual  thing,  bailing  tanks.  Only  Cornish  and 
compressed-air  pumps  will  work  with  any  security  when  drowned, 
and  electrical  pumps  are  easily  ruined. 

General  Power  Conditions.  —  The  question  of  pumping  in- 
stallation is  much  dependent  upon  the  power  installation  and 
other  power  requirements  of  the  mine.  For  instance,  where 
electrical  power  is  purchased  or  generated  by  water-power,  then 
electrical  pumps  have  every  advantage.  Or  where  a  large 
number  of  subsidiary  motors  can  be  economically  driven  from 
one  central  steam-  or  gas-driven  electrical  generation  plant, 
they  again  have  a  strong  call,  —  especially  if  the  amount  of  water 
to  be  handled  is  moderate.  Where  the  water  is  of  limited  volume 
and  compressed-air  plant  a  necessity  for  the  mine,  then  air- 
driven  pumps  may  be  the  most  advantageous,  etc. 

Mechanical  Efficiency.  —  The  mechanical  efficiency  of  drain- 
age machinery  is  very  largely  a  question  of  method  of  power  ap- 
plication. The  actual  pump  can  be  built  to  almost  the  same 
efficiency  for  any  power  application,  and  with  the  exception  of 


140  PRINCIPLES  OF  MINING. 

the  limited  field  of  bailing  with  tanks,  mechanical  drainage  is  a 
matter  of  pumps.  All  pumps  must  be  set  below  their  load,  bar- 
ring a  few  possible  feet  of  suction  lift,  and  they  are  therefore 
perforce  underground,  and  in  consequence  all  power  must  be 
transmitted  from  the  surface.  Transmission  itself  means  loss  of 
power  varying  from  10  to  60%,  depending  upon  the  medium  used. 
It  is  therefore  the  choice  of  transmission  medium  that  largely 
governs  the  mechanical  efficiency. 

Systems  of  Drainage.  —  The  ideal  pumping  system  for  metal 
mines  would  be  one  which  could  be  built  in  units  and  could  be 
expanded  or  contracted  unit  by  unit  with  the  fluctuation  in 
volume;  which  could  also  be  easily  moved  to  meet  the  differ- 
ences of  lifts;  and  in  which  each  independent  unit  could  be  of 
the  highest  mechanical  efficiency  and  would  require  but  little 
space  for  erection.  Such  an  ideal  is  unobtainable  among  any  of 
the  appliances  with  which  the  writer  is  familiar. 

The  wide  variations  in  the  origin  of  power,  in  the  form  of 
transmission,  and  in  the  method  of  final  application,  and  the  many 
combinations  of  these  factors,  meet  the  demands  for  flexibility, 
efficiency,  capital  cost,  and  reliability  in  various  degrees  depend- 
ing upon  the  environment  of  the  mine.  Power  nowadays  is 
generated  primarily  with  steam,  water,  and  gas.  These  origins 
admit  the  transmission  of  power  to  the  pumps  by  direct  steam, 
compressed  air,  electricity,  rods,  or  hydraulic  columns. 

Direct  Steam-pumps.  —  Direct  steam  has  the  disadvantage 
of  radiated  heat  in  the  workings,  of  loss  by  the  radiation,  and, 
worse  still,  of  the  impracticability  of  placing  and  operating  a 
highly  efficient  steam-engine  underground.  It  is  all  but  im- 
possible to  derive  benefit  from  the  vacuum,  as  any  form  of  sur- 
face condenser  here  is  impossible,  and  there  can  be  no  return  of 
the  hot  soft  water  to  the  boilers. 

Steam-pumps  fall  into  two  classes,  rotary  and  direct-acting; 
the  former  have  the  great  advantage  of  permitting  the  use  of 
steam  expansively  and  affording  some  field  for  effective  use  of 
condensation,  but  they  are  more  costly,  require  much  room,  and 
are  not  fool-proof.  The  direct-acting  pumps  have  all  the  advan- 
tage of  compactness  and  the  disadvantage  of  being  the  most 


MECHANICAL  EQUIPMENT.  141 

inefficient  of  pumping  machines  used  in  mining.  Taking  the 
steam  consumption  of  a  good  surface  steam  plant  at  15  pounds 
per  horse-power  hour,  the  efficiency  of  rotary  pumps  with  well- 
insulated  pipes  is  probably  not  over  50%,  and  of  direct-acting 
pumps  from  40%  down  to  10%. 

The  advantage  of  all  steam-pumps  lies  in  the  low  capital 
outlay,  —  hence  their  convenient  application  to  experimental 
mining  and  temporary  pumping  requirements.  For  final  equip- 
ment they  afford  a  great  deal  of  flexibility,  for  if  properly  con- 
structed they  can  be,  with  slight  alteration,  moved  from  one 
horizon  to  another  without  loss  of  relative  efficiency.  Thus  the 
system  can  be  rearranged  for  an  increased  volume  of  water,  by 
decreasing  the  lift  and  increasing  the  number  of  pumps  from 
different  horizons. 

Compressed-air  Pumps.  —  Compressed-air  transmission  has 
an  application  similar  to  direct  steam,  but  it  is  of  still  lower 
mechanical  efficiency,  because  of  the  great  loss  in  compression. 
It  has  the  superiority  of  not  heating  the  workings,  and  there  is 
no  difficulty  as  to  the  disposal  of  the  exhaust,  as  with  steam. 
Moreover,  such  pumps  will  work  when  drowned.  Compressed 
air  has  a  distinct  place  for  minor  pumping  units,  especially  those 
removed  from  the  shaft,  for  they  can  be  run  as  an  adjunct  to 
the  air-drill  system  of  the  mine,  and  by  this  arrangement  much 
capital  outlay  may  be  saved.  The  cost  of  the  extra  power  con- 
sumed by  such  an  arrangement  is  less  than  the  average  cost  of 
compressed-air  power,  because  many  of  the  compressor  charges 
have  to  be  paid  anyway.  When  compressed  air  is  water-gener- 
ated, they  have  a  field  for  permanent  installations.  The  effi- 
ciency of  even  rotary  air-driven  pumps,  based  on  power  deliv- 
ered into  a  good  compressor,  is  probably  not  over  25%. 

Electrical  Pumps.  —  Electrical  pumps  have  somewhat  less 
flexibility  than  steam-  or  air-driven  apparatus,  in  that  the  speed 
of  the  pumps  can  be  varied  only  within  small  limits.  They  have 
the  same  great  advantage  in  the  easy  reorganization  of  the  sys- 
tem to  altered  conditions  of  water-flow.  Electricity,  when  steam- 
generated,  has  the  handicap  of  the  losses  of  two  conversions, 
the  actual  pump  efficiency  being  about  60%  in  well-constructed 


142  PRINCIPLES   OF  MINING. 

plants;  the  efficiency  is  therefore  greater  than  direct  steam  or 
compressed  air.  Where  the  mine  is  operated  with  water-power, 
purchased  electric  current,  or  where  there  is  an  installation  of 
electrical  generating  plant  by  steam  or  gas  for  other  purposes, 
electrically  driven  pumps  take  precedence  over  all  others  on 
account  of  their  combined  moderate  capital  outlay,  great  flexi- 
bility, and  reasonable  efficiency. 

In  late  years,  direct-coupled,  electric-driven  centrifugal 
pumps  have  entered  the  mining  field,  but  their  efficiency,  despite 
makers'  claims,  is  low.  While  they  show  comparatively  good 
results  on  low  lifts  the  slip  increases  with  the  lift.  In  heads 
over  200  feet  their  efficiency  is  probably  not  30%  of  the  power 
delivered  to  the  electrical  generator.  Their  chief  attractions  are 
small  capital  cost  and  the  compact  size  which  admits  of  easy 
installation. 

Rod-driven  Pumps.  —  Pumps  of  the  Cornish  type  in  vertical 
shafts,  if  operated  to  full  load  and  if  driven  by  modern  engines, 
have  an  efficiency  much  higher  than  any  other  sort  of  installa- 
tion, and  records  of  85  to  90%  are  not  unusual.  The  highest 
efficiency  in  these  pumps  yet  obtained  has  been  by  driving  the 
pump  with  rope  transmission  from  a  high-speed  triple  expan- 
sion engine,  and  in  this  plant  an  actual  consumption  of  only  17 
pounds  of  steam  per  horse-power  hour  for  actual  water  lifted 
has  been  accomplished. 

To  provide,  however,  for  increase  of  flow  and  change  of 
horizon,  rod-driven  pumps  must  be  so  overpowered  at  the  earlier 
stage  of  the  mine  that  they  operate  with  great  loss.  Of  all 
pumping  systems  they  are  the  most  expensive  to  provide.  They 
have  no  place  in  crooked  openings  and  only  work  in  inclines  with 
many  disadvantages. 

In  general  their  lack  of  flexibility  is  fast  putting  them  out  of 
the  metal  miner's  purview.  Where  the  pumping  depth  and 
volume  of  water  are  approximately  known,  as  is  often  the  case 
in  coal  mines,  this,  the  father  of  all  pumps,  still  holds  its  own. 

Hydraulic  Pumps.  —  Hydraulic  pumps,  in  which  a  column 
of  water  is  used  as  the  transmission  fluid  from  a  surface  pump  to 
a  corresponding  pump  underground  has  had  some  adoption  in 


MECHANICAL  EQUIPMENT. 


143 


coal  mines,  but  little  in  metal  mines.  They  have  a  certain 
amount  of  flexibility  but  low  efficiency,  and  are  not  likely  to  have 
much  field  against  electrical  pumps. 

Bailing.  —  Bailing  deserves  to  be  mentioned  among  drainage 
methods,  for  under  certain  conditions  it  is  a  most  useful  system, 
and  at  all  times  a  mine  should  be  equipped  with  tanks  against 
accident  to  the  pumps.  Where  the  amount  of  water  is  limited, 
-  up  to,  say,  50,000  gallons  daily,  —  and  where  the  ore  output  of 
the  mine  permits  the  use  of  the  winding-engine  for  part  of  the 
time  on  water  haulage,  there  is  in  the  method  an  almost  total 
saving  of  capital  outlay.  Inasmuch  as  the  winding-engine,  even 
when  the  ore  haulage  is  finished  for  the  day,  must  be  under  steam 
for  handling  men  in  emergencies,  and  as  the  labor  of  stokers, 
engine-drivers,  shaft-men,  etc.,  is  therefore  necessary,  the  cost 
of  power  consumed  by  bailing  is  not  great,  despite  the  low  effi- 
ciency of  winding-engines. 

Comparison  of  Various  Systems.  —  If  it  is  assumed  that 
flexibility,  reliability,  mechanical  efficiency,  and  capital  cost  can 
each  be  divided  into  four  figures  of  relative  importance,  —  A,  B,  C, 
and  D,  with  A  representing  the  most  desirable  result,  —  it  is  pos- 
sible to  indicate  roughly  the  comparative  values  of  various  pump- 
ing systems.  It  is  not  pretended  that  the  four  degrees  are  of 
equal  import.  In  all  cases  the  factor  of  general  power  conditions 
on  the  mine  may  alter  the  relative  positions. 


DIRECT 
STEAM 

COMPRESSED 

ELEC- 

STEAM- 
DRIVEN 

HYDRAU- 
LIC 

BAILING 

PUMPS 

AIR 

TRICITY 

RODS 

COLUMNS 

TANKS 

Flexibility  .     . 

A 

A 

B 

D 

B 

A 

Reliability  .     . 

B 

B 

B 

A 

D 

A 

Mechanical 

Efficiency  . 

C 

D 

B 

A 

C 

D 

Capital  Cost    . 

A 

B 

B 

D 

D 

—- 

As  each  mine  has  its  special  environment,  it  is  impossible  to 
formulate  any  final  conclusion  on  a  subject  so  involved.  The 
attempt  would  lead  to  a  discussion  of  a  thousand  supposititious 


144  PRINCIPLES  OF  MINING. 

cases  and  hypothetical  remedies.  Further,  the  description  alone 
of  pumping  machines  would  fill  volumes,  and  the  subject  will 
never  be  exhausted.  The  engineer  confronted  with  pumping 
problems  must  marshal  all  the  alternatives,  count  his  money, 
and  apply  the  tests  of  flexibility,  reliability,  efficiency,  and  cost, 
choose  the  system  of  least  disadvantages,  and  finally  deprecate  the 
whole  affair,  for  it  is  but  a  parasite  growth  on  the  mine. 


CHAPTER  XIV. 
MECHANICAL  EQUIPMENT  (Concluded). 

MACHINE  DRILLING  I    POWER  TRANSMISSION  J    COMPRESSED  AIR  VS. 

ELECTRICITY;    AIR   DRILLS;    MACHINE   vs.   HAND   DRILLING. 

WORK-SHOPS.      IMPROVEMENT   IN   EQUIPMENT. 

FOR  over  two  hundred  years  from  the  introduction  of  drill- 
holes for  blasting  by  Caspar  Weindel  in  Hungary,  to  the  invention 
of  the  first  practicable  steam  percussion  drill  by  J.  J.  Crouch  of 
Philadelphia,  in  1849,  all  drilling  was  done  by  hand.  Since 
Crouch's  time  a  host  of  mechanical  drills  to  be  actuated  by  all 
sorts  of  power  have  come  forward,  and  even  yet  the  machine- 
drill  has  not  reached  a  stage  of  development  where  it  can  dis- 
place hand-work  under  all  conditions.  Steam-power  was  never 
adapted  to  underground  work,  and  a  serviceable  drill  for  this 
purpose  was  not  found  until  compressed  air  for  transmission  was 
demonstrated  by  Dommeiller  on  the  Mt.  Cenis  tunnel  in  1861. 

The  ideal  requirements  for  a  drill  combine :  — 

a.  Power  transmission  adapted  to  underground  conditions. 

6.  Lightness. 

c.  Simplicity  of  construction. 

d.  Strength. 

e.  Rapidity  and  strength  of  blow. 
/.  Ease  of  erection. 

g.  Reliability. 

h.  Mechanical  efficiency. 

i.  Low  capital  cost. 

No  drill  invented  yet  fills  all  these  requirements,  and  all  are  a 
compromise  on  some  point. 

Power  Transmission;  Compressed  Air  vs.  Electricity.  —  The 
only  transmissions  adapted  to  underground  drill-work  are  com- 

145 


146  PRINCIPLES  OF  MINING. 

pressed  air  and  electricity,  and  as  yet  an  electric-driven  drill  has 
not  been  produced  which  meets  as  many  of  the  requirements  of 
the  metal  miner  as  do  compressed-air  drills.  The  latter,  up  to 
date,  have  superiority  in  simplicity,  lightness,  ease  of  erection,  reli- 
ability, and  strength  over  electric  machines.  Air  has  another 
advantage  in  that  it  affords  some  assistance  to  ventilation,  but 
it  has  the  disadvantage  of  remarkably  low  mechanical  efficiency. 
The  actual  work  performed  by  the  standard  3  J -inch  air-drill 
probably  does  not  amount  to  over  two  or  three  horse-power 
against  from  fifteen  to  eighteen  horse-power  delivered  into  the 
compressor,-  or  mechanical  efficiency  of  less  than  25%.  As 
electrical  power  can  be  delivered  to  the  drill  with  much  less 
loss  than  compressed  air,  the  field  for  a  more  economical  drill 
on  this  line  is  wide  enough  to  create  eventually  the  proper  tool 
to  apply  it.  The  most  satisfactory  electric  drill  produced  has 
been  the  Temple  drill,  which  is  really  an  air-drill  driven  by  a 
small  electrically-driven  compressor  placed  near  the  drill  itself. 
But  even  this  has  considerable  deficiencies  in  mining  work;  the 
difficulties  of  setting  up,  especially  for  stoping  work,  and  the  more 
cumbersome  apparatus  to  remove  before  blasting  are  serious 
drawbacks.  It  has  deficiencies  in  reliability  and  greater  com- 
plication of  machinery  than  direct  air. 

Air-compression.  —  The  method  of  air-compression  so  long 
accomplished  only  by  power-driven  pistons  has  now  an  al- 
ternative in  some  situations  by  the  use  of  falling  water.  This 
latter  system  is  a  development  of  the  last  twelve  years,  and, 
due  to  the  low  initial  outlay  and  extremely  low  operating  costs, 
bids  fair  in  those  regions  where  water  head  is  available  not  only 
to  displace  the  machine  compressor,  but  also  to  extend  the  appli- 
cation of  compressed  air  to  mine  motors  generally,  and  to  stay  in 
some  environments  the  encroachment  of  electricity  into  the  com- 
pressed-air field.  Installations  of  this  sort  in  the  West  Kootenay, 
B.C.,  and  at  the  Victoria  copper  mine,  Michigan,  are  giving 
results  worthy  of  careful  attention. 

Mechanical  air-compressors  are  steam-,  water-,  electrical-, 
and  gas-driven,  the  alternative  obviously  depending  on  the 
source  and  cost  of  power.  Electrical-  and  gas-  and  water- 


MECHANICAL  EQUIPMENT.  147 

driven  compressors  work  under  the  disadvantage  of  constant 
speed  motors  and  respond  little  to  the  variation  in  load,  a  par- 
tial remedy  for  which  lies  in  enlarged  air-storage  capacity. 
Inasmuch  as  compressed  air,  so  far  as  our  knowledge  goes  at 
present,  must  be  provided  for  drills,  it  forms  a  convenient  trans^ 
mission  of  power  to  various  motors  underground,  such  as  small 
pumps,  winches,  or  locomotives.  As  stated  in  discussing  those 
machines,  it  is  not  primarily  a  transmission  of  even  moderate 
mechanical  efficiency  for  such  purposes ;  but  as  against  the  in- 
stallation and  operation  of  independent  transmission,  such  as 
steam  or  electricity,  the  economic  advantage  often  compensates 
the  technical  losses.  Where  such  motors  are  fixed,  as  in  pumps 
and  winches,  a  considerable  gain  in  efficiency  can  be  obtained 
by  reheating. 

It  is  not  proposed  to  enter  a  discussion  of  mechanical  details 
of  air-compression,  more  than  to  call  attention  to  the  most  com- 
mon delinquency  in  the  installation  of  such  plants.  This  defi- 
ciency lies  in  insufficient  compression  capacity  for  the  needs  of 
the  mine  and  consequent  effective  operation  of  drills,  for  with 
under  75  pounds  pressure  the  drills  decrease  remarkably  in 
rapidity  of  stroke  and  force  of  the  blow.  The  consequent  de- 
crease in  actual  accomplishment  is  far  beyond  the  ratio  that 
might  be  expected  on  the  basis  of  mere  difference  of  pressure. 
Another  form  of  the  same  chronic  ill  lies  in  insufficient  air-storage 
capacity  to  provide  for  maintenance  of  pressure  against  moments 
when  all  drills  or  motors  in  the  mine  synchronize  in  heavy  de- 
mand for  air,  and  thus  lower  the  pressure  at  certain  periods. 

Air-drills.  —  Air-drills  are  from  a  mechanical  point  of  view 
broadly  of  two  types,  —  the  first,  in  which  the  drill  is  the  piston 
extension;  and  the  second,  a  more  recent  development  for  min- 
ing work,  in  which  the  piston  acts  as  a  hammer  striking  the 
head  of  the  drill.  From  an  economic  point  of  view  drills  may 
be  divided  into  three  classes.  First,  heavy  drills,  weighing  from 
150  to  400  pounds,  which  require  two  men  for  their  operation; 
second,  "baby"  drills  of  the  piston  type,  weighing  from  110  to 
150  pounds,  requiring  one  man  with  occasional  assistance  in 
setting  up;  and  third,  very  light  drills  almost  wholly  of  the 


148  PRINCIPLES  OF  MINING. 

hammer  type.  This  type  is  built  in  two  forms :  a  heavier  type 
for  mounting  on  columns,  weighing  about  80  pounds ;  and  a  type 
after  the  order  of  the  pneumatic  riveter,  weighing  as  low  as  20 
pounds  and  worked  without  mounting. 

The  weight  and  consequent  mobility  of  a  drill,  aside  from 
labor  questions,  have  a  marked  .effect  on  costs,  for  the  lighter  the 
drill  the  less  difficulty  and  delay  in  erection,  and  consequent 
less  loss  of  time  and  less  tendency  to  drill  holes  from  one  radius, 
regardless  of  pointing  to  take  best  advantage  of  breaking  planes. 
Moreover,  smaller  diameter  and  shorter  holes  consume  less 
explosives  per  foot  advanced  or  per  ton  broken.  The  best  re- 
sults in  tonnage  broken  and  explosive  consumed,  if  measured  by 
the  foot  of  drill-hole  necessary,  can  be  accomplished  from  hand- 
drilling  and  the  lighter  the  machine  drill,  assuming  equal  reliabil- 
ity, the  nearer  it  approximates  these  advantages. 

The  blow,  and  therefore  size  and  depth  of  hole  and  rapidity 
of  drilling,  are  somewhat  dependent  upon  the  size  of  cylinders 
and  length  of  stroke,  and  therefore  the  heavier  types  are  better 
adapted  to  hard  ground  and  to  the  deep  holes  of  some  develop- 
ment points.  Their  advantages  over  the  other  classes  lie  chiefly 
in  this  ability  to  bore  exceedingly  hard  material  and  in  the 
greater  speed  of  advance  possible  in  development  work ;  but  ex- 
cept for  these  two  special  purposes  they  are  not  as  economical 
per  foot  advanced  or  per  ton  of  ore  broken  as  the  lighter  drills. 

The  second  class,  where  men  can  be  induced  to  work  them 
one  man  per  drill,  saves  in  labor  and  gains  in  mobility.  Many 
tests  show  great  economy  of  the  "baby"  type  of  piston  drills 
in  average  ground  over  the  heavier  machines  for  stoping  and 
for  most  lateral  development.  All  piston  types  are  somewhat 
cumbersome  and  the  heavier  types  require  at  least  four  feet  of 
head  room.  The  "baby"  type  can  be  operated  in  less  space 
than  this,  but  for  narrow  stopes  they  do  not  lend  themselves  with 
the  same  facility  as  the  third  class. 

The  third  class  of  drills  is  still  in  process  of  development,  but 
it  bids  fair  to  displace  much  of  the  occupation  of  the  piston  types 
of  drill.  Aside  from  being  a  one-man  drill,  by  its  mobility  it 
will  apparently  largely  reproduce  the  advantage  of  hand-drilling 


MECHANICAL  EQUIPMENT.  149 

in  ability  to  place  short  holes  from  the  most  advantageous  angles 
and  for  use  in  narrow  places.  As  compared  with  other  drills  it 
bids  fair  to  require  less  time  for  setting  up  and  removal  and  for 
change  of  bits;  to  destroy  less  steel  by  breakages;  to  dull  the 
bits  less  rapidly  per  foot  of  hole;  to  be  more  economical  of 
power;  to  require  much  less  skill  in  operation,  for  judgment  is  less 
called  upon  in  delivering  speed ;  and  to  evade  difficulties  of  fissured 
ground,  etc.  And  finally  the  cost  is  only  one-half,  initially  and 
for  spares.  Its  disadvantage  so  far  is  a  lack  of  reliability  due 
to  lightness  of  construction,  but  this  is  very  rapidly  being  over- 
come. This  type,  however,  is  limited  in  depth  of  hole  possible, 
for,  from  lack  of  positive  reverse  movement,  there  is  a  tendency 
for  the  spoil  to  pack  around  the  bit,  and  as  a  result  about  four 
feet  seems  the  limit. 

The  performance  of  a  machine-drill  under  show  conditions 
may  be  anything  up  to  ten  or  twelve  feet  of  hole  per  hour  on 
rock  such  as  compact  granite ;  but  in  underground  work  a  large 
proportion  of  the  time  is  lost  in  picking  down  loose  ore,  setting 
up  machines,  removal  for  blasting,  clearing  away  spoil,  making 
adjustments,  etc.  The  amount  of  lost  time  is  often  dependent 
upon  the  width  of  stope  or  shaft  and  the  method  of  stoping. 
Situations  which  require  long  drill  columns  or  special  scaffolds 
greatly  accentuate  the  loss  of  time.  Further,  the  difficulties  in 
setting  up  reflect  indirectly  on  efficiency  to  a  greater  extent 
in  that  a  larger  proportion  of  holes  are  drilled  from  one  radius 
and  thus  less  adapted  to  the  best  breaking  results  than  where 
the  drill  can  easily  be  reset  from  various  angles. 

The  usual  duty  of  a  heavy  drill  per  eight-hour  shift  using 
two  men  is  from  20  to  40  feet  of  hole,  depending  upon  the  rock, 
facilities  for  setting  up,  etc.,  etc.*  The  lighter  drills  have  a  less 
average  duty,  averaging  from  15  to  25  feet  per  shift. 

Machine  vs.  Hand-Drilling.  —  The  advantages  of  hand-drilling 
over  machine-drilling  lie,  first,  in  the  total  saving  of  power,  the  ab- 
sence of  capital  cost,  repairs,  depreciation,  etc.,  on  power,  com- 

*Over  the  year  1907  in  twenty-eight  mines  compiled  from  Alaska  to 
Australia,  an  average  of  23.5  feet  was  drilled  per  eight-hour  shift  by  ma- 
chines larger  than  three-inch  cylinder. 


150  PRINCIPLES  OF  MINING. 

presser  and  drill  plant;  second,  the  time  required  for  setting  up 
machine-drills  does  not  warrant  frequent  blasts,  so  that  a  number 
of  holes  on  one  radius  are  a  necessity,  and  therefore  machine-holes 
generally  cannot  be  pointed  to  such  advantage  as  hand-holes. 
Hand-holes  can  be  set  to  any  angle,  and  by  thus  frequent  blasting 
yield  greater  tonnage  per  foot  of  hole.  Third,  a  large  number 
of  comparative  statistics  from  American,  South  African,  and 
Australian  mines  show  a  saving  of  about  25%  in  explosives  for 
the  same  tonnage  or  foot  of  advance  by  hand-holes  over  medium 
and  heavy  drill-holes. 

The  duty  of  a  skilled  white  man,  single-handed,  in  rock 
such  as  is  usually  met  below  the  zone  of  oxidation,  is  from  5 
to  7  feet  per  shift,  depending  on  the  rock  and  the  man.  Two 
men  hand-drilling  will  therefore  do  from  £  to  f  of  the  same 
footage  of  holes  that  can  be  done  by  two  men  with  a  heavy 
machine-drill,  and  two  men  hand-drilling  will  do  from  £  to  | 
the  footage  of  two  men  with  two  light  drills. 

The  saving  in  labor  of  from  75  to  33%  by  machine-drilling 
may  or  may  not  be  made  up  by  the  other  costs  involved  in 
machine-work.  The  comparative  value  of  machine-  and  hand- 
drilling  is  not  subject  to  sweeping  generalization.  A  large 
amount  of  data  from  various  parts  of  the  world,  with  skilled 
white  men,  shows  machine-work  to  cost  from  half  as  much  per 
ton  or  foot  advanced  as  hand- work  to  25%  more  than  hand- 
work, depending  on  the  situation,  type  of  drill,  etc.  In  a  general 
way  hand-work  can  more  nearly  compete  with  heavy  machines 
than  light  ones.  The  situations  where  hand-work  can  compete 
with  even  light  machines  are  in  very  narrow  stopes  where  drills 
cannot  be  pointed  to  advantage,  and  where  the  increased  work- 
ing space  necessary  for  machine  drills  results  in  breaking  more 
waste.  Further,  hand-drilling  can  often  compete  with  machine- 
work  in  wide  stopes  where  long  columns  or  platforms  must 
be  used  and  therefore  there  is  much  delay  in  taking  down, 
reerection,  etc. 

Many  other  factors  enter  into  a  comparison,  however,  for 
machine-drilling  produces  a  greater  number  of  deeper  holes  and 
permits  larger  blasts  and  therefore  more  rapid  progress.  In  driv- 


MECHANICAL  EQUIPMENT.  151 

ing  levels  under  average  conditions  monthly  footage  is  from  two 
to  three  times  as  great  with  heavy  machines  as  by  hand-drilling, 
and  by  lighter  machines  a  somewhat  less  proportion  of  greater 
speed.  The  greater  speed  obtained  in  development  work,  the 
.greater  tonnage  obtained  per  man  in  stoping,  with  consequent 
reduction  in  the  number  of  men  employed,  and  in  reduction 
of  superintendence  and  general  charges  are  indirect  advantages 
for  machine-drilling  not  to  be  overlooked. 

The  results  obtained  in  South  Africa  by  hand-drilling  in  shafts, 
and  its  very  general  adoption  there,  seem  to  indicate  that  better 
speed  and  more  economical  work  can  be  obtained  in  that  way 
in  very  large  shafts  than  by  machine-drilling.  How  far  special 
reasons  there  apply  to  smaller  shafts  or  labor  conditions  else- 
where have  yet  to  be  demonstrated.  In  large-dimension  shafts 
demanding  a  large  number  of  machines,  the  handling  of  long 
machine  bars  and  machines  generally  results  in  a  great  loss  of 
time.  The  large  charges  in  deep  holes  break  the  walls  very 
irregularly;  misfires  cause  more  delay;  timbering  is  more 
difficult  in  the  face  of  heavy  blasting  charges;  and  the  larger 
amount  of  spoil  broken  at  one  time  delays  renewed  drilling,  and 
altogether  the  advantages  seem  to  lie  with  hand-drilling  in 
shafts  of  large  horizontal  section. 

The  rapid  development  of  special  drills  for  particular  condi- 
tions has  eliminated  the  advantage  of  hand-work  in  many  situa- 
tions during  the  past  ten  years,  and  the  invention  of  the  hammer 
type  of  drill  bids  fair  to  render  hand-drilling  a  thing  of  the  past. 
One  generalization  is  possible,  and  that  is,  if  drills  are  run  on  40- 
50  pounds'  pressure  they  are  no  economy  over  hand-drilling. 

WORKSHOPS. 

In  addition  to  the  ordinary  blacksmithy,  which  is  a  necessity, 
the  modern  tendency  has  been  to  elaborate  the  shops  on  mines 
to  cover  machine-work,  pattern-making  and  foundry-work,  in 
order  that  delays  may  be  minimized  by  quick  repairs.  To  provide, 
however,  for  such  contingencies  a  staff  of  men  must  be  kept 
larger  than  the  demand  of  average  requirements.  The  result 


152  PRINCIPLES  OF  MINING. 

is  an  effort  to  provide  jobs  or  to  do  work  extravagantly  or  un- 
necessarily well.  In  general,  it  is  an  easy  spot  for  fungi  to  start 
growing  on  the  administration,  and  if  custom  repair  shops  are 
available  at  all,  mine  shops  can  be  easily  overdone. 

A  number  of  machines  are  now  in  use  for  sharpening  drills. 
Machine-sharpening  is  much  cheaper  than  hand-work,  although 
the  drills  thus  sharpened  are  rather  less  efficient  owing  to  the 
difficulty  of  tempering  them  to  the  same  nicety;  however,  the 
net  results  are  in  favor  of  the  machines. 


IMPROVEMENT   IN   EQUIPMENT. 

Not  only  is  eveiy  mine  a  progressive  industry  until  the  bot- 
tom gives  out,  but  the  technology  of  the  industry  is  always  pro- 
gressing, so  that  the  manager  is  almost  daily  confronted  with 
improvements  which  could  be  made  in  his  equipment  that 
would  result  in  decreasing  expenses  or  increasing  metal  recovery. 
There  is  one  test  to  the  advisability  of  such  alterations :  How 
long  will  it  take  to  recover  the  capital  outlay  from  the  savings 
effected  ?  and  over  and  above  this  recovery  of  capital  there  must 
be  some  very  considerable  gain.  The  life  of  mines  is  at  least 
secured  over  the  period  exposed  in  the  ore-reserves,  and  if  the 
proposed  alteration  will  show  its  recovery  and  profit  in  that 
period,  then  it  is  certainly  justified  .  If  it  takes  longer  than  this 
on  the  average  speculative  ore-deposit,  it  is  a  gamble  on  finding 
further  ore.  As  a  matter  of  practical  policy  it  will  be  found  that 
an  improvement  in  equipment  which  requires  more  than  three  or 
four  years  to  redeem  itself  out  of  saving,  is  usually  a  mechanical 
or  metallurgical  refinement  the  indulgence  in  which  is  very 
doubtful. 


CHAPTER  XV. 
RATIO  OF  OUTPUT  TO  THE  MINE. 

DETERMINATION  OF  THE  POSSIBLE  MAXIMUM;  LIMITING  FAC- 
TORS ;  COST  OF  EQUIPMENT ;  LIFE  OF  THE  MINE  J  MECHANICAL 
INEFFICIENCY  OF  PATCHWORK  PLANT;  OVERPRODUCTION  OF 
BASE  METAL;  SECURITY  OF  INVESTMENT. 

THE  output  obtainable  from  a  given  mine  is  obviously  de- 
pendent not  only  on  the  size  of  the  deposit,  but  also  on  the  equip- 
ment provided,  —  in  which  equipment  means  the  whole  working 
appliances,  surface  and  underground. 

A  rough  and  ready  idea  of  output  possibilities  of  inclined 
deposits  can  be  secured  by  calculating  the  tonnage  available  per 
foot  of  depth  from  the  horizontal  cross-section  of  the  ore-bodies 
exposed  and  assuming  an  annual  depth  of  exhaustion,  or  in  hori- 
zontal deposits  from  an  assumption  of  a  given  area  of  exhaus- 
tion. Few  mines,  at  the  time  of  initial  equipment,  are  developed 
to  an  extent  from  which  their  possibilities  in  production  are  evi- 
dent, for  wise  finance  usually  leads  to  the  erection  of  some  equip- 
ment and  production  before  development  has  been  advanced  to 
a  point  that  warrants  a  large  or  final  installation.  Moreover, 
even  were  the  full  possibilities  of  the  mine  known,  the  limitations 
of  finance  usually  necessitate  a  less  plant  to  start  with  than  is 
finally  contemplated.  Therefore  output  and  equipment  are  usu- 
ally growing  possibilities  during  the  early  life  of  a  mine. 

There  is  no  better  instance  in  mine  engineering  where  pure 
theory  must  give  way  to  practical  necessities  of  finance  than  in 
the  determination  of  the  size  of  equipment  and  therefore  output. 
Moreover,  where  finance  even  is  no  obstruction,  there  are  other 
limitations  of  a  very  practical  order  which  must  dominate  the 
question  of  the  size  of  plant  giving  the  greatest  technical  economy. 
It  is,  however,  useful  to  state  the  theoretical  considerations  in 
determining  the  ultimate  volume  of  output  and  therefore  the 
size  of  equipments,  for  the  theory  will  serve  to  illuminate  the 

153 


154  PRINCIPLES  OF  MINING. 

practical  limitations.  The  discussion  will  also  again  demonstrate 
that  all  engineering  is  a  series  of  compromises  with  natural  and 
economic  forces. 

Output  giving  Least  Production  Cost.  —  As  one  of  the  most 
important  objectives  is  to  work  the  ore  at  the  least  cost  per 
ton,  it  is  not  difficult  to  demonstrate  that  the  minimum  work- 
ing costs  can  be  obtained  only  by  the  most  intensive  pro- 
duction. To  prove  this,  it  need  only  be  remembered  that  the 
working  expenses  of  a  mine  are  of  two  sorts :  one  is  a  factor  of 
the  tonnage  handled,  such  as  stoping  and  ore-dressing;  the  other 
is  wholly  or  partially  dependent  upon  time.  A  large  number 
of  items  are  of  this  last  order.  Pumping  and  head-office  expenses 
are  almost  entirely  charges  independent  of  the  tonnage  handled. 
Superintendence  and  staff  salaries  and  the  like  are  in  a  large 
proportion  dependent  upon  time.  Many  other  elements  of 
expense,  such  as  the  number  of  engine-drivers,  etc.,  do  not 
increase  proportionately  to  increase  in  tonnage.  These  charges, 
or  the  part  of  them  dependent  upon  time  apart  from  tonnage, 
may  be  termed  the  "fixed  charges." 

There  is  another  fixed  charge  more  obscure  yet  no  less  certain. 
Ore  standing  in  a  mine  is  like  money  in  a  bank  drawing  no  inter- 
est, and  this  item  of  interest  may  be  considered  a  "  fixed  charge/' 
for  if  the  ore  were  realized  earlier,  this  loss  could  be  partially 
saved.  This  subject  is  further  referred  to  under  "  Amortization." 

If,  therefore,  the  time  required  to  exhaust  the  mine  be  pro- 
longed by  the  failure  to  maintain  the  maximum  output,  the  total 
cost  of  working  it  will  be  greater  by  the  fixed  charges  over  such 
an  increased  period.  Conversely,  by  equipping  on  a  larger 
scale,  the  mine  will  be  exhausted  more  quickly,  a  saving  in  total 
cost  can  be  made,  and  the  ultimate  profit  can  be  increased  by 
an  amount  corresponding  to  the  time  saved  from  the  ravages  of 
fixed  charges.  In  fine,  the  working  costs  may  be  reduced  by 
larger  operations,  and  therefore  the  value  of  the  mine  increased. 

The  problem  in  practice  usually  takes  the  form  of  the  relative 
superiority  of  more  or  of  fewer  units  of  plant,  and  it  can  be  con- 
sidered in  more  detail  if  the  production  be  supposed  'to  consist 
of  units  averaging  say  100  tons  per  day  each.  The  advantage  of 


RATIO  OF  OUTPUT  TO  THE  MINE.  155 

more  units  over  less  will  be  that  the  extra  ones  can  be  produced 
free  of  fixed  charges,  for  these  are  an  expense  already  involved 
in  the  lesser  units.  This  extra  production  will  also  enjoy  the 
interest  which  can  be  earned  over  the  period  of  its  earlier  pro- 
duction. Moreover,  operations  on  a  larger  scale  result  in  various 
minor  economies  throughout  the  whole  production,  not  entirely 
included  in  the  type  of  expenditure  mentioned  as  "  fixed  charges." 
We  may  call  these  various  advantages  the  "saving  of  fixed 
charges"  due  to  larger-scale  operations.  The  saving  of  fixed 
charges  amounts  to  very  considerable  sums.  In  general  the 
items  of  working  cost  alone,  mentioned  above,  which  do  not 
increase  proportionately  to  the  tonnage,  aggregate  from  10  to 
25%  of  the  total  costs.  Where  much  pumping  is  involved,  the 
percentage  will  become  even  greater. 

The  question  of  the  value  of  the  mine  as  affected  by  the 
volume  of  output  becomes  very  prominent  in  low-grade  mines, 
where,  if  equipped  for  output  on  too  small  a  scale,  no  profits  at 
all  could  be  earned,  and  a  sufficient  production  is  absolutely 
imperative  for  any  gain.  There  are  many  mines  in  every  country 
which  with  one-third  of  their  present  rate  of  production  would 
lose  money.  That  is,  the  fixed  charges,  if  spread  over  small 
output,  would  be  so  great  per  ton  that  the  profit  would  be 
extinguished  by  them. 

In  the  theoretical  view,  therefore,  it  would  appear  clear  that 
the  greatest  ultimate  profit  from  a  mine  can  be  secured  only  by 
ore  extraction  under  the  highest  pressure.  As  a  corollary  to  this 
it  follows  that  development  must  proceed  with  the  maximum 
speed.  Further,  it  follows  that  the  present  value  of  a  mine  is  at 
least  partially  a  factor  of  the  volume  of  output  contemplated. 


FACTORS    LIMITING    THE    OUTPUT. 

Although  the  above  argument  can  be  academically  defended, 
there  are,  as  said  at  the  start,  practical  limitations  to  the  max- 
imum intensity  of  production,  arising  out  of  many  other  consid- 
erations to  which  weight  must  be  given.  In  the  main,  there  are 
five  principal  limitations :  — 


156  PRINCIPLES  OF  MINING. 

1.  Cost  of  equipment. 

2.  Life  of  the  mine. 

3.  Mechanical  inefficiency  of  patchwork  plant. 

4.  Overproduction  of  base  metal. 

5.  Security  of  investment. 

Cost  of  Equipment.  — The  " saving  of  fixed  charges"  can  only 
be  obtained  by  larger  equipment,  which  represents  an  investment. 
Mining  works,  shafts,  machinery,  treatment  plants,  and  all  the 
paraphernalia  cost  large  sums  of  money.  They  become  either 
worn  out  or  practically  valueless  through  the  exhaustion  of  the 
mines.  Even  surface  machinery  when  in  good  condition  will 
seldom  realize  more  than  one-tenth  of  its  expense  if  useless  at 
its  original  site.  All  mines  are  ephemeral ;  therefore  virtually  the 
entire  capital  outlay  of  such  works  must  be  redeemed  during  the 
life  of  the  mine,  and  the  interest  on  it  must  also  be  recovered. 

The  certain  life,  with  the  exception  of  banket  and  a  few 
other  types  of  deposit,  is  that  shown  by  the  ore  in  sight,  plus 
something  for  extension  of  the  deposit  beyond  exposures.  So, 
against  the  " savings"  to  be  made,  must  be  set  the  cost  of  ob- 
taining them,  for  obviously  it  is  of  no  use  investing  a  dollar  to 
save  a  total  of  ninety  cents.  The  economies  by  increased  pro- 
duction are,  however,  of  such  an  important  character  that  the 
cost  of  almost  any  number  of  added  units  (within  the  ability 
of  the  mine  to  supply  them)  can  be  redeemed  from  these 
savings  in  a  few  years.  For  instance,  in  a  Californian  gold 
mine  where  the  working  expenses  are  $3  and  the  fixed  charges 
are  at  the  low  rate  of  30  cents  per  ton,  one  unit  of  increased 
production  would  show  a  saving  of  over  $10,000  per  annum 
from  the  saving  of  fixed  charges.  In  about  three  years  this 
sum  would  repay  the  cost  of  the  additional  treatment  equip- 
ment. If  further  shaft  capacity  were  required,  the  period  would 
be  much  extended.  On  a  Western  copper  mine,  where  the  costs 
are  $8  and  the  fixed  charges  are  80  cents  per  ton,  one  unit  of 
increased  production  would  effect  a  saving  of  the  fixed  charges 
equal  to  the  cost  of  the  extra  unit  in  about  three  years.  That 
is,  the  total  sum  would  amount  to  $80,000,  or  enough  to  provide 


RATIO  OF  OUTPUT  TO  THE  MINE.  157 

almost  any  type  of  mechanical  equipment  for  such  additional 
tonnage. 

The  first  result  of  vigorous  development  is  to  increase  the  ore 
in  sight,  —  the  visible  life  of  the  mine.  When  such  visible  life 
has  been  so  lengthened  that  the  period  in  which  the  "  saving  of 
fixed  charges'7  will  equal  the  amount  involved  in  expansion  of 
equipment,  then  from  the  standpoint  of  this  limitation  only 
is  the  added  installation  justified.  The  equipment  if  expanded 
on  this  practice  will  grow  upon  the  heels  of  rapid  development 
until  the  maximum  production  from  the  mine  is  reached,  and  a 
kind  of  equilibrium  establishes  itself. 

Conversely,  this  argument  leads  to  the  conclusion  that,  re- 
gardless of  other  considerations,  an  equipment,  and  therefore 
output,  should  not  be  expanded  beyond  the  redemption  by 
way  of  " saving  from  fixed  charges"  of  the  visible  or  certain  life 
of  the  mine.  In  those  mines,  such  as  at  the  Witwatersrand, 
where  there  is  a  fairly  sound  assurance  of  definite  life,  it  is 
possible  to  calculate  at  once  the  size  of  plant  which  by 
saving  of  " fixed  charges"  will  be  eventually  the  most  economi- 
cal, but  even  here  the  other  limitations  step  in  to  vitiate  such 
policy  of  management,  —  chiefly  the  limitation  through  security 
of  investment. 

Life  of  the  Mine.  —  If  carried  to  its  logical  extreme,  the 
above  program  means  a  most  rapid  exhaustion  of  the  mine.  The 
maximum  output  will  depend  eventually  upon  the  rapidity  with 
which  development  work  may  be  extended.  As  levels  and  other 
subsidiary  development  openings  can  be  prepared  in  inclined 
deposits  much  more  quickly  than  the  shaft  can  be  sunk,  the 
critical  point  is  the  shaft-sinking.  As  a  shaft  may  by  exertion 
be  deepened  at  least  400  feet  a  year  on  a  going  mine,  the  pro- 
vision of  an  equipment  to  eat  up  the  ore-body  at  this  rate  of 
sinking  means  very  early  exhaustion  indeed.  In  fact,  had  such 
a  theory  of  production  been  put  into  practice  by  our  forefathers, 
the  mining  profession  might  find  difficulty  in  obtaining  em- 
ployment to-day.  Such  rapid  exhaustion  would  mean  a  depletion 
of  the  mineral  resources  of  the  state  at  a  pace  which  would  be 
alarming. 


158  PRINCIPLES   OF  MINING. 

Mechanical  Inefficiency  of  Patchwork  Plant.  —  Mine  equip- 
ments on  speculative  mines  (the  vast  majority)  are  often  enough 
patchwork,  for  they  usually  grow  from  small  beginnings;  but 
any  scheme  of  expansion  based  upon  the  above  doctrine  would 
need  to  be  modified  to  the  extent  that  additions  could  be  in  units 
large  in  ratio  to  previous  installations,  or  their  patchwork  char- 
acter would  be  still  further  accentuated.  It  would  be  impossible 
to  maintain  mechanical  efficiency  under  detail  expansion. 

Overproduction  of  Base  Metal.  —  Were  this  intensity  of  pro- 
duction of  general  application  to  base  metal  mines  it  would  flood 
the  markets,  and,  by  an  overproduction  of  metal  depress  prices 
to  a  point  where  the  advantages  of  such  large-scale  operations 
would  quickly  vanish.  The  theoretical  solution  in  this  situation 
would  be,  if  metals  fell  below  normal  prices,  let  the  output  be 
reduced,  or  let  the  products  be  stored  until  the  price  recovers. 
From  a  practical  point  of  view  either  alternative  is  a  policy 
difficult  to  face. 

In  the  first  case,  reduction  of  output  means  an  increase  of 
working  expenses  by  the  spread  of  fixed  charges  over  less  tonnage, 
and  this  in  the  face  of  reduced  metal  prices.  It  may  be  con- 
tended, however,  that  a  falling  metal  market  is  usually  the  accom- 
paniment of  a  drop  in  all  commodities,  wherefore  working  costs 
can  be  reduced  somewhat  in  such  times  of  depression,  thereby 
partially  compensating  the  other  elements  making  for  increased 
costs.  Falls  in  commodities  are  also  the  accompaniment  of  hard 
times.  Consideration  of  one's  workpeople  and  the  wholesale 
slaughter  of  dividends  to  the  then  needy  stockholders,  result- 
ing from  a  policy  of  reduced  production,  are  usually  sufficient 
deterrents  to  diminished  output. 

The  second  alternative,  that  of  storing  metal,  means 
equally  a  loss  of  dividends  by  the  investment  of  a  large  sum  in 
unrealized  products,  and  the  interest  on  this  sum.  The  detri- 
ment to  the  market  of  large  amounts  of  unsold  metal  renders  such 
a  course  not  without  further  disadvantages. 

Security  of  Investment.  —  Another  point  of  view  antagonistic 
to  such  wholesale  intensity  of  production,  and  one  worthy  of 
careful  consideration,  is  that  of  the  investor  in  mines.  The  root- 


RATIO  OF  OUTPUT  TO  THE  MINE.  159 

value  of  mining  stocks  is,  or  should  be,  the  profit  in  sight.  If 
the  policy  of  greatest  economy  in  production  costs  be  followed 
as  outlined  above,  the  economic  limit  of  ore-reserves  gives  an 
apparently  very  short  life,  for  the  ore  in  sight  will  never  represent 
a  life  beyond  the  time  required  to  justify  more  plant.  Thus  the 
"economic  limit  of  ore  in  reserve"  will  be  a  store  equivalencing 
a  period  during  which  additional  equipment  can  be  redeemed 
from  the  "  saving  of  fixed  charges,"  or  three  or  four  years, 
usually. 

The  investor  has  the  right  to  say  that  he  wants  the  guarantee 
of  longer  life  to  his  investment,  —  he  will  in  effect  pay  insurance 
for  it  by  a  loss  of  some  ultimate  profit.  That  this  view, 
contradictory  to  the  economics  of  the  case,  is  not  simply  aca- 
demic, can  be  observed  by  any  one  who  studies  what  mines  are 
in  best  repute  on  any  stock  exchange.  All  engineers  must  wish 
to  have  the  industry  under  them  in  high  repute.  The  writer 
knows  of  several  mines  paying  20%  on  their  stocks  which  yet 
stand  lower  in  price  on  account  of  short  ore-reserves  than  mines 
paying  less  annual  returns.  The  speculator,  who  is  an  element 
not  to  be  wholly  disregarded,  wishes  a  rise  in  his  mining  stock, 
and  if  development  proceeds  at  a  pace  in  advance  of  production, 
he  will  gain  a  legitimate  rise  through  the  increase  in  ore- 
reserves. 

The  investor's  and  speculator's  idea  of  the  desirability  of  a 
proved  long  life  readily  supports  the  technical  policy  of  high- 
pressure  development  work,  but  not  of  expansion  of  production, 
for  they  desire  an  increasing  ore-reserve.  Even  the  metal  opera- 
tor who  is  afraid  of  overproduction  does  not  object  to  increased 
ore-reserves.  On  the  point  of  maximum  intensity  of  development 
work  in  a  mine  all  views  coincide.  The  mining  engineer,  if  he 
takes  a  Machiavellian  view,  must  agree  with  the  investor  and  the 
metal  dealer,  for  the  engineer  is  a  "  fixed  charge  "  the  continuance 
of  which  is  important  to  his  daily  needs. 

The  net  result  of  all  these  limitations  is  therefore  an  invariable 
compromise  upon  some  output  below  the  possible  maximum. 
The  initial  output  to  be  contemplated  is  obviously  one  upon 
which  the  working  costs  will  be  low  enough  to  show  a  margin  of 


160  PRINCIPLES  OF  MINING. 

profit.  The  medium  between  these  two  extremes  is  determin- 
able  by  a  consideration  of  the  limitations  set  out,  —  and  the  cash 
available.  When  the  volume  of  output  is  once  determined,  it 
must  be  considered  as  a  factor  in  valuation,  as  discussed  under 
"  Amortization." 


CHAPTER  XVI. 

ADMINISTRATION. 

LABOR  EFFICIENCY;  SKILL;  INTELLIGENCE;  APPLICATION  CO- 
ORDINATION; CONTRACT  WORK;  LABOR  UNIONS;  REAL 
BASIS  OF  WAGES. 

THE  realization  from  a  mine  of  the  profits  estimated  from 
the  other  factors  in  the  case  is  in  the  end  dependent  upon  the 
management.  Good  mine  management  is  based  upon  three 
elementals:  first,  sound  engineering;  second,  proper  coordination 
and  efficiency  of  every  human  unit;  third,  economy  in  the  pur- 
chase and  consumption  of  supplies. 

The  previous  chapters  have  been  devoted  to  a  more  or  less 
extended  exposition  of  economic  engineering.  While  the  second 
and  third  requirements  are-  equally  important,  they  range  in 
many  ways  out  of  the  engineering  and  into  the  human  field. 
For  this  latter  reason  no  complete  manual  will  ever  be  pub- 
lished upon  "  How  to  become  a  Good  Mine  Manager." 

It  is  purposed,  however,  to  analyze  some  features  of  these 
second  and  third  fundamentals,  especially  in  their  interdependent 
phases,  and  next  to  consider  the  subject  of  mine  statistics,  for  the 
latter  are  truly  the  microscopes  through  which  the  competence  of 
the  administration  must  be  examined. 

The  human  unite  in  mine  organization  can  be  divided  into 
officers  and  men.  The  choice  of  mine  officers  is  the  assembling 
of  specialized  brains.  Their  control,  stimulation,  and  inspiration 
is  the  main  work  of  the  administrative  head.  Success  in  the 
selection  and  control  of  staff  is  the  index  of  executive  ability. 
There  are  no  mathematical,  mechanical,  or  chemical  formulas  for 
dealing  with  the  human  mind  or  human  energies. 

Labor.  —  The  whole  question  of  handling  labor  can  be  re- 
duced to  the  one  term  "efficiency."  Not  only  does  the  actual 
labor  outlay  represent  from  60  to  70%  of  the  total  under- 

161 


162  PRINCIPLES  OF  MINING. 

ground  expenses,  but  the  capacity  or  incapacity  of  its  units  is 
responsible  for  wider  fluctuations  in  production  costs  than  the 
bare  predominance  in  expenditure  might  indicate.  The  remain- 
ing expense  is  for  supplies,  such  as  dynamite,  timber,  steel, 
power,  etc.,  and  the  economical  application  of  these  materials 
by  the  workman  has  the  widest  bearing  upon  their  consumption. 

Efficiency  of  the  mass  is  the  resultant  of  that  of  each  indi- 
vidual under  a  direction  which  coordinates  effectively  all  units. 
The  lack  of  effectiveness  in  one  individual  diminishes  the  returns 
not  simply  from  that  man  alone;  it  lowers  the  results  from  num- 
bers of  men  associated  with  the  weak  member  through  the  delay- 
ing and  clogging  of  their  work,  and  of  the  machines  operated  by 
them.  Coordination  of  work  is  a  necessary  factor  of  final 
efficiency.  This  is  a  matter  of  organization  and  administration. 
The  most  zealous  stoping-gang  in  the  world  if  associated  with 
half  the  proper  number  of  truckers  must  fail  to  get  the  desired 
result. 

Efficiency  in  the  single  man  is  the  product  of  three  factors,  — 
skill,  intelligence,  and  application.  .A  great  proportion  of  under- 
ground work  in  a  mine  is  of  a  type  which  can  be  performed  after 
a  fashion  by  absolutely  unskilled  and  even  unintelligent  men,  as 
witness  the  breaking-in  of  savages  of  low  average  mentality, 
like  the  South  African  Kaffirs.  Although  most  duties  can  be 
performed  by  this  crudest  order  of  labor,  skill  and  intelligence 
can  be  applied  to  it  with,  such  economic  results  as  to  compensate 
for  the  difference  in  wage.  The  reason  for  this  is  that  the  last 
fifty  years  have  seen  a  substitution  of  labor-saving  machines  for 
muscle.  Such  machines  displace  hundreds  of  raw  laborers.  Not 
only  do  they  initially  cost  large  sums,  but  they  require  large 
expenditure  for  power  and  up-keep.  These  fixed  charges  against 
the  machine  demand  that  it  shall  be  worked  at  its  maximum. 
For  interest,  power,  and  up-keep  go  on  in  any  event,  and  the 
saving  on  crude  labor  displaced  is  not  so  great  but  that  it  quickly 
disappears  if  the  machine  is  run  under  its  capacity.  To  get  its 
greatest  efficiency,  a  high  degree  of  skill  and  intelligence  is  re- 
quired. Nor  are  skill  and  intelligence  alone  applicable  to 
labor-saying  devices  themselves,  because  drilling  and  blasting 


ADMINISTRATION.  163 

rock  and  executing  other  works  underground  are  matters  in 
which  experience  and  judgment  in  the  individual  workman  count 
to  the  highest  degree. 

How  far  skill  affects  production  costs  has  had  a  thorough 
demonstration  in  West  Australia.  For  a  time  after  the  opening 
of  those  mines  only  a  small  proportion  of  experienced  men  were 
obtainable.  During  this  period  the  rock  broken  per  man  em- 
ployed underground  did  not  exceed  the  rate  of  300  tons  a  year. 
In  the  large  mines  it  has  now,  after  some  eight  years,  attained 
600  to  700  tons. 

How  far  intelligence  is  a  factor  indispensable  to  skill  can  be 
well  illustrated  by  a  comparison  of  the  results  obtained  from 
working  labor  of  a  low  mental  order,  such  as  Asiatics  and  negroes, 
with  those  achieved  by  American  or  Australian  miners.  In  a 
general  way,  it  may  be  stated  with  confidence  that  the  white 
miners  above  mentioned  can,  under  the  same  physical  con- 
ditions, and  with  from  five  to  ten  times  the  wage,  produce 
the  same  economic  result,  —  that  is,  an  equal  or  lower  cost  per 
unit  of  production.  Much  observation  and  experience  in  working 
Asiatics  and  negroes  as  well  as  Americans  and  Australians  in 
mines,  leads  the  writer  to  the  conclusion  that,  averaging  actual 
results,  one  white  man  equals  from  two  to  three  of  the  colored 
races,  even  in  the  simplest  forms  of  mine  work  such  as  shoveling 
or  tramming.  In  the  most  highly  skilled  branches,  such  as 
mechanics,  the  average  ratio  is  as  one  to  seven,  or  in  extreme 
cases  even  eleven.  The  question  is  not  entirely  a  comparison 
of  bare  efficiency  individually;  it  is  one  of  the  sum  total  of  results. 
In  mining  work  the  lower  races  require  a  greatly  increased  amount 
of  direction,  and  this  excess  of  supervisors  consists  of  men  not 
in  themselves  directly  productive.  There  is  always,  too,  a  waste 
of  supplies,  more  accidents,  and  more  ground  to  be  kept  open 
for  accommodating  increased  staff,  and  the  maintenance  of  these 
openings  must  be  paid  for.  There  is  an  added  expense  for 
handling  larger  numbers  in  and  out  of  the  mine,  and  the  lower 
intelligence  reacts  in  many  ways  in  lack  of  coordination  and 
inability  to  take  initiative.  Taking  all  divisions  of  labor 
together,  the  ratio  of  efficiency  as  measured  in  amount  of  output 


164 


PRINCIPLES  OF  MINING. 


works  out  from  four  to  five  colored  men  as  the  equivalent  of  one 
white  man  of  the  class  stated.  The  ratio  of  costs,  for  reasons 
already  mentioned,  and  in  other  than  quantity  relation,  figures 
still  more  in  favor  of  the  higher  intelligence. 

The  following  comparisons,  which  like  all  mine  statistics  must 
necessarily  be  accepted  with  reservation  because  of  some  dissimi- 
larity of  economic  surroundings,  are  yet  on  sufficiently  common 
ground  to  demonstrate  the  main  issue,  —  that  is,  the  bearing  of 
inherent  intelligence  in  the  workmen  and  their  consequent  skill. 
Four  groups  of  gold  mines  have  been  taken,  from  India,  West 
Australia,  South  Africa,  and  Western  America.  All  of  those 
chosen  are  of  the  same  stoping  width,  4  to  5  feet.  All  are  work- 
ing in  depth  and  with  every  labor-saving  device  available.  All 
dip  at  about  the  same  angle  and  are  therefore  in  much  the  same 
position  as  to  handling  rock.  The  other  conditions  are  against 
the  white-manned  mines  and  in  favor  of  the  colored.  That  is, 
the  Indian  mines  have  water-generated  electric  power  and  South 
Africa  has  cheaper  fuel  than  either  the  American  or  Australian 
examples.  In  both  the  white-manned  groups,  the  stopes  are 
supported,  while  in  the  others  no  support  is  required. 


AVERAGE 

NUMBER 

COST  PER 

TONS  OF  MATERIAL 

OF  MEN  J 

EMPLOYED 

TONS  PER 

GROUP  OF  MINES 

EXCAVATED   OVER 

MAN  PER 

PERIOD  COMPILED  | 

ANNUM 

Colored 

White 

Four  Kolar  mines  *  .  . 

963,950 

13,611 

302 

69.3 

$3.85 

Six  Australian  mines  f 

1,027,718 

— 

1,534 

669.9 

2.47 

Three  Witwatersrand 

mines  t  

2  962  640 

13  560 

1,595 

195.5 

2.68 

Five  American  mines  § 

1,089,500 

1,524 

713.3 

1.92 

*  Indian  wages  average  about  20  cents  per  day. 

t  White  men's  wages  average  about  $3  per  day. 

$  About  two-fifths  of  the  colored  workers  were  negroes,  and  three-fifths  Chinamen.  Negroes 
average  about  60  cents,  and  Chinamen  about  45  cents  per  day,  including  keep. 

§  Wages  about  $3.50.     Tunnel  entry  in  two  mines. 

E  Includes  rock  broken  in  development  work. 

In  the  case  of  the  specified  African  mines,  the  white  labor  is  employed  almost  wholly  in  positions 
of  actual  or  semi-superintendence,  such  as  one  white  man  in  charge  of  two  or  three  drills. 

In  the  Indian  case,  in  addition  to  the  white  men  who  are  wholly  in  superintendence,  there  were 
of  the  natives  enumerated  some  1000  in  positions  of  semi  superintendence,  as  contractors  or 
headmen,  working-gangers,  etc. 


ADMINISTRATION.  165 

One  issue  arises  out  of  these  facts,  and  that  is  that  no  en- 
gineer or  investor  in  valuing  mines  is  justified  in  anticipating 
lower  costs  in  regions  where  cheap  labor  exists. 

In  supplement  to  sheer  skill  and  intelligence,  efficiency  can 
be  gained  only  by  the  application  of  the  man  himself.  A  few 
months  ago  a  mine  in  California  changed  managers.  The  new 
head  reduced  the  number  employed  one-third  without  impair- 
ing the  amount  of  work  accomplished.  This  was  not  the  result 
of  higher  skill  or  intelligence  in  the  men,  but  in  the  manager. 
Better  application  and  coordination  were  secured  from  the 
working  force.  Inspiration  to  increase  of  exertion  is  created 
less  by  "driving''  than  by  recognition  of  individual  effort,  in 
larger  pay,  and  by  extending  justifiable  hope  of  promotion.  A 
great  factor  in  the  proficiency  of  the  mine  manager  is  his  abil- 
ity to  create  an  esprit-de-corps  through  the  whole  staff,  down  to 
the  last  tool  boy.  Friendly  interest  in  the  welfare  of  the  men 
and  stimulation  by  competitions  between  various  works  and 
groups  all  contribute  to  this  end. 

Contract  Work.  —  The  advantage  both  to  employer  and  em- 
ployed of  piece  work  over  wage  needs  no  argument.  In  a  gen- 
eral way,  contract  work  honorably  carried  out  puts  a  premium 
upon  individual  effort,  and  thus  makes  for  efficiency.  There 
are  some  portions  of  mine  work  which  cannot  be  contracted, 
but  the  development,  stoping,  and  trucking  can  be  largely 
managed  in  this  way,  and  these  items  cover  65  to  75%  of  the 
total  labor  expenditure  underground. 

In  development  there  are  two  ways  of  basing  contracts,  —  the 
first  on  the  footage  of  holes  drilled,  and  the  second  on  the  foot- 
age of  heading  advanced.  In  contract-stoping  there  are  four 
methods  depending  on  the  feet  of  hole  drilled,  on  tonnage,  on 
cubic  space,  and  on  square  area  broken. 

All  these  systems  have  their  rightful  application,  conditioned 
upon  the  class  of  labor  and  character  of  the  deposit.  • 

In  the  "hole"  system,  the  holes  are  "pointed"  by  some 
mine  official  and  are  blasted  by  a  special  crew.  The  miner 
therefore  has  little  interest  in  the  result  of  the  breaking.  If  he 
is  a  skilled  white  man,  the  hours  which  he  has  wherein  to  con- 


166  PRINCIPLES   OF  MINING. 

template  the  face  usually  enable  him  to  place  holes  to  better 
advantage  than  the  occasional  visiting  foreman.  With  colored 
labor,  the  lack  of  intelligence  in  placing  holes  and  blasting  usu- 
ally justifies  contracts  per  "foot  drilled."  Then  the  holes  are 
pointed  and  blasted  by  superintending  men. 

On  development  work  with  the  foot-hole  system,  unless  two 
working  faces  can  be  provided  for  each  contracting  party,  they 
are  likely  to  lose  time  through  having  finished  their  round  of 
holes  before  the  end  of  the  shift.  As  blasting  must  be  done 
outside  the  contractor's  shifts,  it  means  that  one  shift  per  day 
must  be  set  aside  for  the  purpose.  Therefore  not  nearly  such 
progress  can  be  made  as  where  working  the  face  with  three 
shifts.  For  these  reasons,  the  "hole"  system  is  not  so  advan- 
tageous in  development  as  the  "foot  of  advance"  basis. 

In  stoping,  the  "hole"  system  has  not  only  a  wider,  but  a 
sounder  application.  In  large  ore-bodies  where  there  are  waste 
inclusions,  it  has  one  superiority  over  any  system  of  excavation 
measurement,  namely,  that  the  miner  has  no  interest  in  break- 
ing waste  into  the  ore. 

The  plan  of  contracting  stopes  by  the  ton  has  the  disad- 
vantage that  either  the  ore  produced  by  each  contractor  must 
be  weighed  separately,  or  truckers  must  be  trusted  to  count 
correctly,  and  to  see  that  the  cars  are  full.  Moreover,  trucks 
must  be  inspected  for  waste,  —  a  thing  hard  to  do  underground. 
So  great  are  these  detailed  difficulties  that  many  mines  are  send- 
ing cars  to  the  surface  in  cages  when  they  should  be  equipped 
for  bin-loading  and  self-dumping  skips. 

The  method  of  contracting  by  the  cubic  foot  of  excavation 
saves  all  necessity  for  determining  the  weight  of  the  output  of 
each  contractor.  Moreover,  he  has  no  object  in  mixing  waste 
with  the  ore,  barring  the  breaking  of  the  walls.  This  system 
therefore  requires  the  least  superintendence,  permits  the  modern 
type  of  hoisting,  and  therefore  leaves  little  justification  for  the 
survival  of  the  tonnage  basis. 

Where  veins  are  narrow,  stoping  under  contract  by  the  square 
foot  or  fathom  measured  parallel  to  the  walls  has  an  advantage. 
The  miner  has  no  object  then  in  breaking  wall-rock,  and  the 


ADMINISTRATION.  167 

thoroughness  of  the  ore-extraction  is  easily  determined  by  in- 
spection. 

Bonus  Systems.  —  By  giving  cash  bonuses  for  special  ac- 
complishment, much  the  same  results  can  be  obtained  in  some 
departments  as  by  contracting.  A  bonus  per  foot  of  heading 
gained  above  a  minimum,  or  an  excess  of  trucks  trammed  beyond 
a  minimum,  or  prizes  for  the  largest  amount  done  during  the 
week  or  month  in  special  works  or  in  different  shifts,  —  all  these 
have  a  useful  application  in  creating  efficiency.  A  high  level  of 
results  once  established  is  easily  maintained. 

Labor  Unions.  —  There  is  another  phase  of  the  labor  ques- 
tion which  must  be  considered  and  that  is  the  general  relations 
of  employer  and  employed.  In  these  days  of  largely  corporate 
proprietorship,  the  owners  of  mines  are  guided  in  their  relations 
with  labor  by  engineers  occupying  executive  positions.  On  them 
falls  the  responsibility  in  such  matters,  and  the  engineer  becomes 
thus  a  buffer  between  labor  and  capital.  As  corporations  have 
grown,  so  likewise  have  the  labor  unions.  In  general,  they  are 
normal  and  proper  antidotes  for  unlimited  capitalistic  organiza- 
tion. 

Labor  unions  usually  pass  through  two  phases.  First,  the 
inertia  of  the  unorganized  labor  is  too  often  stirred  only  by 
demagogic  means.  After  organization  through  these  and  other 
agencies,  the  lack  of  balance  in  the  leaders  often  makes  for  in- 
justice in  demands,  and  for  violence  to  obtain  them  and  dis- 
regard of  agreements  entered  upon.  As  time  goes  on,  men 
become  educated  in  regard  to  the  rights  of  their  employers,  and 
to  the  reflection  of  these  rights  in  ultimate  benefit  to  labor  itself. 
Then  the  men,  as  well  as  the  intelligent  employer,  endeavor  to 
safeguard  both  interests.  When  this  stage  arrives,  violence  dis- 
appears in  favor  of  negotiation  on  economic  principles,  and  the 
unions  achieve  their  greatest  real  gains.  Given  a  union  with 
leaders  who  can  control  the  members,  and  who  are  disposed  to 
approach  differences  in  a  business  spirit,  there  are  few  sounder 
positions  for  the  employer,  for  agreements  honorably  carried  out 
dismiss  the  constant  harassments  of  possible  strikes.  Such 
unions  exist  in  dozens  of  trades  in  this  country,  and  they  are 


168  PRINCIPLES  OF  MINING. 

entitled  to  greater  recognition.  The  time  when  the  employer 
could  ride  roughshod  over  his  labor  is  disappearing  with  the 
doctrine  of  "laissez  faire"  on  which  it  was  founded.  The 
sooner  the  fact  is  recognized,  the  better  for  the  employer.  The 
sooner  some  miners'  unions  develop  from  the  first  into  the  second 
stage,  the  more  speedily  will  their  organizations  secure  general 
respect  and  influence.* 

The  crying  need  of  labor  unions,  and  of  some  employers  as 
well,  is  education  on  a  fundamental  of  economics  too  long  dis- 
regarded by  all  classes  and  especially  by  the  academic  economist. 
When  the  latter  abandon  the  theory  that  wages  are  the  result 
of  supply  and  demand,  and  recognize  that  in  these  days  of  in- 
ternational flow  of  labor,  commodities  and  capital,  the  real  con- 
trolling factor  in  wages  is  efficiency,  then  such  an  educational 
campaign  may  become  possible.  Then  will  the  employer  and 
employee  find  a  common  ground  on  which  each  can  benefit. 
There  lives  no  engineer  who  has  not  seen  insensate  dispute  as  to 
wages  where  the  real  difficulty  was  inefficiency.  No  adminis- 
trator begrudges  a  division  with  his  men  of  the  increased  profit 
arising  from  increased  efficiency.  But  every  administrator  be- 
grudges the  wage  level  demanded  by  labor  unions  whose  policy 
is  decreased  efficiency  in  the  false  belief  that  they  are  providing 
for  more  labor. 

*  Some  years  of  experience  with  compulsory  arbitration  in  Australia 
and  New  Zealand  are  convincing  that  although  the  law  there  has  many 
defects,  still  it  is  a  step  in  the  right  direction,  and  the  result  has  been  of 
almost  unmixed  good  to  both  sides.  One  of  its  minor,  yet  really  great, 
benefits  has  been  a  considerable  extinction  of  the  parasite  who  lives  by 
creating  violence. 


CHAPTER  XVII. 

ADMINISTRATION  (Continued). 

ACCOUNTS  AND  TECHNICAL  DATA  AND  REPORTS;  WORKING  COSTS J 
DIVISION  OF  EXPENDITURE;  INHERENT  LIMITATIONS  IN  .AC- 
CURACY OF  WORKING  COSTS;  WORKING  COST  SHEETS. 
GENERAL  TECHNICAL  DATA;  LABOR,  SUPPLIES,  POWER, 
SURVEYS,  SAMPLING,  AND  ASSAYING. 

FIRST  and  foremost,  mine  accounts  are  for  guidance  in  the 
distribution  of  expenditure  and  in  the  collection  of  revenue; 
secondly,  they  are  to  determine  the  financial  progress  of  the 
enterprise,  its  profit  or  loss;  and  thirdly,  they  are  to  furnish 
statistical  data  to  assist  the  management  in  its  interminable 
battle  to  reduce  expenses  and  increase  revenue,  and  to  enable  the 
owner  to  determine  the  efficiency  of  his  administrators.  Book- 
keeping per  se  is  no  part  of  this  discussion.  The  fundamental 
purpose  of  that  art  is  to  cover  the  first  two  objects,  and,  as  such, 
does  not  differ  from  its  application  to  other  commercial  concerns. 

In  addition  to  these  accounting  matters  there  is  a  further  type 
of  administrative  report  of  equal  importance — that  is  the 
periodic  statements  as  to  the  physical  condition  of  the  property, 
the  results  of  exploration  in  the  mine,  and  the  condition  of  the 
equipment. 

ACCOUNTS. 

The  special  features  of  mine  accounting  reports  which  are 
a  development  to  meet  the  needs  of  this  particular  business  are 
the  determination  of  working  costs,  and  the  final  presentation  of 
these  data  in  a  form  available  for  comparative  purposes. 

The  subject  may  be  discussed  under :  — 

1.  Classes  of  mine  expenditure. 

2.  Working  costs. 

169 


170  PRINCIPLES  OF  MINING. 

3.  The  dissection  of  expenditures  depart  mentally. 

4.  Inherent  limitations  in  the  accuracy  of  working  costs. 

5.  Working  cost  sheets. 

In  a  wide  view,  mine  expenditures  fall  into  three  classes, 
which  may  be  termed  the  "  fixed  charges,"  "  proportional  charges," 
and  "suspense  charges"  or  " capital  expenditure."  "Fixed 
charges"  are  those  which,  like  pumping  and  superintendence, 
depend  upon  time  rather  than  tonnage  and  material  handled. 
They  are  expenditures  that  would  not  decrease  relatively  to 
output.  "Proportional  charges"  are  those  which,  like  ore- 
breaking,  stoping,  supporting  stopes,  and  tramming,  are  a 
direct  coefficient  of  the  ore  extracted.  "Suspense  charges"  are 
those  which  are  an  indirect  factor  of  the  cost  of  the  ore  pro- 
duced, such  as  equipment  and  development.  These  expendi- 
tures are  preliminary  to  output,  and  they  thus  represent  a  storage 
of  expense  to  be  charged  off  when  the  ore  is  won.  This  outlay 
is  often  called  "capital  expenditure."  Such  a  term,  though  in 
common  use,  is  not  strictly  correct,  for  the  capital  value  vanishes 
when  the  ore  is  extracted,  but  in  conformity  with  current  usage 
the  term  "capital  expenditure"  will  be  adopted. 

Except  for  the  purpose  of  special  inquiry,  such  as  outlined 
under  the  chapter  on  "Ratio  of  Output,"  "fixed  charges"  are 
not  customarily  a  special  division  in  accounts.  In  a  general  way, 
such  expenditures,  combined  with  the  "proportional  charges," 
are  called  "revenue  expenditure,"  as  distinguished  from  the 
capital,  or  "  suspense, "  expenditures.  In  other  words,  "  revenue  " 
expenditures  are  those  involved  in  the  daily  turnover  of  the  busi- 
ness and  resulting  in  immediate  returns.  The  inherent  differ- 
ence in  character  of  revenue  and  capital  expenditures  is  respon- 
sible for  most  of  the  difficulties  in  the  determination  of  working 
costs,  and  most  of  the  discussion  on  the  subject. 

Working  Costs.  —  "Working  costs"  are  a  division  of  expendi- 
ture for  some  unit,  —  the  foot  of  opening,  ton  of  ore,  a  pound  of 
metal,  cubic  yard  or  fathom  of  material  excavated,  or  some  other 
measure.  The  costs  per  unit  are  usually  deduced  for  each  month 
and  each  year.  They  are  generally  determined  for  each  of  the 


ADMINISTRATION.  171 

different  departments  of  the  mine  or  special  works  separately. 
Further,  the  various  sorts  of  expenditure  in  these  departments 
are  likewise  segregated. 

In  metal  mining  the  ton  is  the  universal  unit  of  distribution 
for  administrative  purpose,  although  the  pound  of  metal  is  often 
used  to  indicate  final  financial  results.  The  object  of  determi- 
nation of  "working  costs"  is  fundamentally  for  comparative 
purposes.  Together  with  other  technical  data,  they  are  the 
nerves  of  the  administration,  for  by  comparison  of  detailed  and 
aggregate  results  with  other  mines  and  internally  in  the  same 
mine,  over  various  periods  and  between  different  works,  a  most 
valuable  check  on  efficiency  is  possible.  Further,  there  is  one 
collateral  value  in  all  statistical  data  not  to  be  overlooked,  which 
is  that  the  knowledge  of  its  existence  induces  in  the  subordinate 
staff  both  solicitude  and  emulation. 

The  fact  must  not  be  lost  sight  of,  however,  that  the  wide 
variations  in  physical  and  economic  environment  are  so  likely 
to  vitiate  conclusions  from  comparisons  of  statistics  from  two 
mines  or  from  two  detailed  works  on  the  same  mine,  or  even  from 
two  different  months  on  the  same  work,  that  the  greatest  care 
and  discrimination  are  demanded  in  their  application.  More- 
over, the  inherent  difficulties  in  segregating  and  dividing  the 
accounts  which  underlie  such  data,  render  it  most  desirable  to 
offer  some  warning  regarding  the  limits  to  which  segregation  and 
division  may  be  carried  to  advantage. 

As  working  costs  are  primarily  for  comparisons,  in  order  that 
they  may  have  value  for  this  purpose  they  must  include  only 
such  items  of  expenditure  as  will  regularly  recur.  If  this  lim- 
itation were  more  generally  recognized,  a  good  deal  of  dispute 
and  polemics  on  the  subject  might  be  saved.  For  this  reason  it 
is  quite  impossible  that  all  the  expenditure  on  the  mine  should 
be  charged  into  working  costs,  particularly  some  items  that 
arise  through  "  capital  expenditure." 

The  Dissection  of  Expenditures  Departmentally.  —  The  final 
division  in  the  dissection  of  the  mine  expenditure  is  in  the 
main :  — 


172 


PRINCIPLES  OF  MINING. 


Revenue.  < 


(1)     General  Expenses. 


Capital 

or 
Suspense. 


(2)     Ore  Extraction. 


Pumping. 


(4)     Development. 


Ore-breaking. 
Supporting  Stopes. 
Trucking  Ore. 
Hoisting. 

Shaft-sinking. 
Station-cutting. 
Crosscutting. 
Driving. 
Rising. 
Winzes. 
.  Diamond  Drilling. , 

(5)     Construction    and ) 

Equipment.       I  Various  Works. 


Various  expendi- 
tures for  labor, 
supplies,  power,  re- 
pairs, etc.,  worked 
out  per  ton  or  foot 
advanced  over  each 
department. 


The  detailed  dissection  of  expenditures  in  these  various  depart- 
ments with  view  to  determine  amount  of  various  sorts  of  ex- 
penditure over  the  department,  or  over  some  special  work  in 
that  department,  is  full  of  unsolvable  complications.  The 
allocation  of  the  direct  expenditure  of  labor  and  supplies  applied 
to  the  above  divisions  or  special  departments  in  them,  is  easily 
accomplished,  but  beyond  this  point  two  sorts  of  difficulties 
immediately  arise  and  offer  infinite  field  for  opinion  and  method. 
The  first  of  these  difficulties  arises  from  supplementary  depart- 
ments on  the  mine,  such  as  "power,"  "repairs  and  maintenance," 
"  sampling  and  assaying."  These  departments  must  be  "  spread  " 
over  the  divisions  outlined  above,  for  such  charges  are  in  part  or 
whole  a  portion  of  the  expense  of  these  divisions.  Further, 
all  of  these  "spread"  departments  are  applied  to  surface  as  well 
as  to  underground  works,  and  must  be  divided  not  only  over 
the  above  departments  but  also  over  the  surface  departments,  — 
not  under  discussion  here.  The  common  method  is  to  distribute 
"power"  on  a  basis  of  an  approximation  of  the  amount  used  in 
each  department;  to  distribute  "repairs  and  maintenance," 
either  on  a  basis  of  shop  returns,  or  a  distribution  over  all  de- 
partments on  the  basis  of  the  labor  employed  in  those  depart- 
ments, on  the  theory  that  such  repairs  arise  in  this  proportion; 
to  distribute  sampling  and  assaying  over  the  actual  points  to 
which  they  relate  at  the  average  cost  per  sample  or  assay. 


ADMINISTRATION.  173 

" General  expenses,"  that  is,  superintendence,  etc.,  are  often 
not  included-  in  the  final  departments  as  above,  but  are  some- 
times " spread"  in  an  attempt  to  charge  a  proportion  of  super- 
intendence to  each  particular  work.  As,  however,  such  "  spread- 
ing" must  take  place  on  the  basis  of  the  relative  expenditure 
in  each  department,  the  result  is  of  little  value,  for  such  a  basis 
does  not  truly  represent  the  proportion  of  general  superintendence, 
etc.,  devoted  to  each  department.  If  they  are  distributed  over 
all  departments,  capital  as  well  as  revenue,  on  the  basis  of 
total  expenditure,  they  inflate  the  " capital  expenditure"  depart- 
ments against  a  day  of  reckoning  when  these  charges  come  to 
be  distributed  over  working  costs.  Although  it  may  be  con- 
tended that  the  capital  departments  also  require  supervision, 
such  a  practice  is  a  favorite  device  for  showing  apparently  low 
working  costs  in  the  revenue  departments.  The  most  coura- 
geous way  is  not  to  distribute  general  expenses  at  all,  but  to 
charge  them  separately  and  directly  to  revenue  accounts  and 
thus  wholly  into  working  costs. 

The  second  problem  is  to  reduce  the  " suspense"  or  capital 
charges  to  a  final  cost  per  ton,  and  this  is  no  simple  matter. 
Development  expenditures  bear  a  relation  to  the  tonnage  devel- 
oped and  not  to  that  extracted  in  any  particular  period.  If  it  is 
desired  to  preserve  any  value  for  comparative  purposes  in  the 
mining  costs,  such  outlay  must  be  charged  out  on  the  basis  of 
the  tonnage  developed,  and  such  portion  of  the  ore  as  is  extracted 
must  be  written  off  at  this  rate ;  otherwise  one  month  may  see 
double  the  amount  of  development  in  progress  which  another 
records,  and  the  underground  costs  would  be  swelled  or  diminished 
thereby  in  a  way  to  ruin  their  comparative  value  from  month  to 
month.  The  ore  developed  cannot  be  satisfactorily  determined 
at  short  intervals,  but  it  can  be  known  at  least  annually,  and  a 
price  may  be  deduced  as  to  its  cost  per  ton.  In  many  mines 
a  figure  is  arrived  at  by  estimating  ore-reserves  at  the  end  of  the 
year,  and  this  figure  is  used  during  the  succeeding  year  as  a 
"redemption  of  development"  and  as  such  charged  to  working 
costs,  and  thus  into  revenue  account  in  proportion  to  the  tonnage 
extracted.  This  matter  is  further  elaborated  in  some  mines, 


174  PRINCIPLES  OF  MINING. 

in  that  winzes  and  rises  are  written  off  at  one  rate;  levels  and 
crosscuts  at  another,  and  shafts  at  one  still  lower,  on  the  theory 
that  they  lost  their  usefulness  in  this  progression  as  the  ore  is 
extracted.  This  course,  however,  is  a  refinement  hardly  war- 
ranted. 

Plant  and  equipment  constitute  another  " suspense"  account 
even  harder  to  charge  up  logically  to  tonnage  costs,  for  it  is  in 
many  items  dependent  upon  the  life  of  the  mine,  which  is  an 
unknown  factor.  Most  managers  debit  repairs  and  maintenance 
directly  to  the  revenue  account  and  leave  the  reduction  of  the 
construction  outlay  to  an  annual  depreciation  on  the  final 
balance  sheet,  on  the  theory  that  the  plant  is  maintained  out  of 
costs  to  its  original  value.  This  subject  will  be  discussed 
further  on. 

Inherent  Limitations  in  Accuracy  of  Working  Costs.  - 
There  are  three  types  of  such  limitations  which  arise  in  the 
determination  of  costs  and  render  too  detailed  dissection  of  such 
costs  hopeless  of  accuracy  and  of  little  value  for  comparative 
purposes.  They  are,  first,  the  difficulty  of  determining  all  of  even 
direct  expenditure  on  any  particular  crosscut,  stope,  haulage, 
etc.;  second,  the  leveling  effect  of  distributing  the  " spread" 
expenditures,  such  as  power,  repairs,  etc.;  and  third,  the  diffi- 
culties arising  out  of  the  borderland  of  various  departments. 

Of  the  first  of  these  limitations  the  instance  may  be  cited 
that  foremen  and  timekeepers  can  indicate  very  closely  the  desti- 
nation of  labor  expense,  and  also  that  of  some  of  the  large  items 
of  supply,  such  as  timber  and  explosives,  but  the  distribution  of 
minor  supplies,  such  as  candles,  drills,  picks,  and  shovels,  is  impos- 
sible of  accurate  knowledge  without  an  expense  wholly  unwar- 
ranted by  the  information  gained.  To  determine  at  a  particular 
crosscut  the  exact  amount  of  steel,  and  of  tools  consumed,  and 
the  cost  of  sharpening  them,  would  entail  their  separate  and 
special  delivery  to  the  same  place  of  attack  and  a  final  weighing-up 
to  learn  the  consumption. 

Of  the  second  sort  of  limitations,  the  effect  of  " spread" 
expenditure,  the  instance  may  be  given  that  the  repairs  and 
maintenance  are  done  by  many  men  at  work  on  timbers,  tracks, 


ADMINISTRATION.  175 

machinery,  etc.  It  is  hopeless  to  try  and  tell  how  much  of  their 
work  should  be  charged  specifically  to  detailed  points.  In  the 
distribution  of  power  may  be  taken  the  instance  of  air-drills. 
Although  the  work  upon  which  the  drill  is  employed  can  be  known, 
the  power  required  for  compression  usually  comes  from  a  common 
power-plant,  so  that  the  portion  of  power  debited  to  the  air 
compressor  is  an  approximation.  The  assumption  of  an  equal 
consumption  of  air  by  all  drills  is  a  further  approximation. 
In  practice,  therefore,  many  expenses  are  distributed  on  the 
theory  that  they  arise  in  proportion  to  the  labor  employed,  or 
the  machines  used  in  the  various  departments.  The  net  result 
is  to  level  down  expensive  points  and  level  up  inexpensive  ones. 

The  third  sort  of  limitation  of  accounting  difficulty  referred 
to,  arises  in  determining  into  which  department  are  actually 
to  be  allocated  the  charges  which  lie  in  the  borderland  between 
various  primaiy  classes  of  expenditure.  For  instance,  in  ore 
won  from  development,  —  in  some  months  three  times  as  much 
development  may  be  in  ore  as  in  other  months.  If  the  total 
expense  of  development  work  which  yields  ore  be  charged  to 
stoping  account,  and  if  cost  be  worked  out  on  the  total  tonnage 
of  ore  hoisted,  then  the  stoping  cost  deduced  will  be  erratic, 
and  the  true  figures  will  be  obscured.  On  the  other  hand,  if 
all  development  is  charged  to  "capital  account  "and  the  stoping 
cost  worked  out  on  all  ore  hoisted,  it  will  include  a  fluctuating 
amount  of  ore  not  actually  paid  for  by  the  revenue  departments 
or  charged  into  costs.  This  fluctuation  either  way  vitiates  the 
whole  comparative  value  of  the  stoping  costs.  In  the  following 
system  a  compromise  is  reached  by  crediting  "  development " 
with  an  amount  representing  the  ore  won  from  development  at 
the  average  cost  of  stoping,  and  by  charging  this  amount  into 
"stoping."  A  number  of  such  questions  arise  where  the  proper 
division  is  simply  a  matter  of  opinion. 

The  result  of  all  these  limitations  is  that  a  point  in  detail 
is  quickly  reached  where  no  further  dissection  of  expenditure 
is  justified,  since  it  becomes  merely  an  approximation.  The 
writer's  own  impression  is  that  without  an  unwarrantable  num- 
ber of  accountants,  no  manager  can  tell  with  any  accuracy  the 


176  PRINCIPLES  OF  MINING. 

cost  of  any  particular  stope,  or  of  any  particular  development 
heading.  Therefore,  aside  from  some  large  items,  such  detailed 
statistics,  if  given,  are  to  be  taken  with  great  reserve. 

Working  Cost  Sheets.  —  There  are  an  infinite  number  of 
forms  of  working  cost  sheets,  practically  every  manager  having 
a  system  of  his  own.  To  be  of  greatest  value,  such  sheets  should 
show  on  their  face  the  method  by  which  the  "spread"  depart- 
ments are  handled,  and  how  revenue  and  suspense  departments 
are  segregated.  When  too  much  detail  is  presented,  it  is  but 
a  waste  of  accounting  and  consequent  expense.  Where  to  draw 
the  line  in  this  regard  is,  however,  a  matter  of  great  difficulty. 
No  cost  sheet  is  entirely  satisfactory. 


GENERAL  TECHNICAL  DATA. 

For  the  purposes  of  efficient  management,  the  information 
gathered  under  this  head  is  of  equal,  if  not  superior,  importance 
to  that  under  "working  costs."  Such  data  fall  generally  under 
the  following  heads :  — 

Labor.  —  Returns  of  the  shifts  worked  in  the  various  depart- 
ments for  each  day  and  for  the  month ;  worked  out  on  a  monthly 
basis  of  footage  progress,  tonnage  produced  or  tons  handled 
per  man;  also  where  possible  the  footage  of  holes  drilled,  worked 
out  per  man  and  per  machine. 

Supplies.  —  Daily  returns  of  supplies  used ;  the  principal 
items  worked  out  monthly  in  quantity  per  foot  of  progress,  or 
per  ton  of  ore  produced. 

Power. — Fuel,  lubricant,  etc.,  consumed  in  steam  production, 
worked  out  into  units  of  steam  produced,  and  this  production 
allocated  to  the  various  engines.  Where  electrical  power  is 
used,  the  consumption  of  the  various  motors  is  set  out. 

Surveys.  —  The  need  of  accurate  plans  requires  no  discus- 
sion. Aside  from  these,  the  survey-office  furnishes  the  returns 


ADMINISTRATION.  177 

of  development  footage,  measurements  under  contracts,  and  the 
like. 

Sampling  and  Assaying.  —  Mine  sampling  and  assaying  fall 
under  two  heads,  —  the  determination  of  the  value  of  standing 
ore,  and  of  products  from  the  mine.  The  sampling  and  assaying 
on  a  going  mine  call  for  the  same  care  and  method  as  in  cases 
of  valuation  of  the  mine  for  purchase,  —  the  details  of  which 
have  been  presented  under  "Mine  Valuation,"  -for  through 
it,  guidance  must  not  only  be  had  to  the  value  of  the  mine  and 
for  reports  to  owners,  but  the  detailed  development  and  ore 
extraction  depend  on  an  absolute  knowledge  of  where  the  values 
lie. 


CHAPTER   XVIII. 
ADMINISTRATION  (Concluded). 

ADMINISTRATIVE    REPORTS. 

IN  addition  to  financial  returns  showing  the  monthly  re- 
ceipts, expenditures,  and  working  costs,  there  must  be  in  proper 
administration  periodic  reports  from  the  officers  of  the  mine  to 
the  owners  or  directors  as  to  the  physical  progress  of  the  enter- 
prise. Such  reports  must  embrace  details  of  ore  extraction, 
metal  contents,  treatment  recoveries,  construction  of  equipment, 
and  the  results  of  underground  development.  The  value  of 
mines  is  so  much  affected  by  the  monthly  or  even  daily  result 
of  exploration  that  reports  of  such  work  are  needed  very  fre- 
quently, —  weekly  or  even  daily  if  critical  work  is  in  progress. 
These  reports  must  show  the  width,  length,  and  value  of  the  ore 
disclosed. 

The  tangible  result  of  development  work  is  the  tonnage 
and  grade  of  ore  opened  up.  How  often  this  stock-taking 
should  take  place  is  much  dependent  upon  the  character  of 
the  ore.  The  result  of  exploration  in  irregular  ore-bodies  often 
does  not,  over  short  periods,  show  anything  tangible  in  definite 
measurable  tonnage,  but  at  least  annually  the  ore  reserve  can 
be  estimated. 

In  mines  owned  by  companies,  the  question  arises  almost 
daily  as  to  how  much  of  and  how  often  the  above  infor- 
mation should  be  placed  before  stockholders  (and  therefore 
the  public)  by  the  director's.  In  a  general  way,  any  company 
whose  shares  are  offered  on  the  stock  exchange  is  indirectly 
inviting  the  public  to  become  partners  in  the  business,  and 
these  partners  are  entitled  to  all  the  information  which  affects  the 
value  of  their  property  and  are  entitled  to  it  promptly.  More- 
over, mining  is  a  business  where  competition  is  so  obscure  and  so 
much  a  matter  of  indifference,  that  suppression  of  important 

178 


ADMINISTRATION.  179 

facts  in  documents  for  public  circulation  has  no  justifica- 
tion. On  the  other  hand,  both  the  technical  progress  of  the 
industry  and  its  position  in  public  esteem  demand  the  fullest 
disclosure  and  greatest  care  in  preparation  of  reports.  Most 
stockholders'  ignorance  of  mining  technology  and  of  details  of 
their  particular  mine  demands  a  great  deal  of  care  and  discretion 
in  the  preparation  of  these  public  reports  that  they  may  not  be 
misled.  Development  results  may  mean  little  or  much,  depend- 
ing upon  the  location  of  the  work  done  in  relation  to  the  ore- 
bodies,  etc.,  and  this  should  be  clearly  set  forth. 

The  best  opportunity  of  clear,  well-balanced  statements  lies 
in  the  preparation  of  the  annual  report  and  accounts.  Such 
reports  are  of  three  parts :  — 

1.  The  "  profit  and  loss  "  account,  or  the  "  revenue  account." 

2.  The  balance   sheet :    that  is,    the  assets   and  liabilities 

statement. 

3.  The  reports  of  the  directors,  manager,  and   consulting 

engineer. 

The  first  two  items  are  largely  matters  of  bookkeeping.  They 
or  the  report  should  show  the  working  costs  per  ton  for  the  year. 
What  must  be  here  included  in  costs  is  easier  of  determination 
than  in  the  detailed  monthly  cost  sheets  of  the  administration; 
for  at  the  annual  review,  it  is  not  difficult  to  assess  the  amount 
chargeable  to  development.  Equipment  expenditure,  however, 
presents  an  annual  difficulty,  for,  as  said,  the  distribution  of  this 
item  is  a  factor  of  the  life  of  the  mine,  and  that  is  unknown.  If 
such  a  plant  has  been  paid  for  out  of  the  earnings,  there  is  no 
object  in  carrying  it  on  the  company's  books  as  an  asset,  and 
most  well-conducted  companies  write  it  off  at  once.  On  the 
other  hand,  'where  the  plant  is  paid  for  out  of  capital  provided 
for  the  purpose,  even  to  write  off  depreciation  means  that  a  cor- 
responding sum  of  cash  must  be  held  in  the  company's  treasury 
in  order  to  balance  the  accounts,  —  in  other  words,  depreciation 
in  such  an  instance  becomes  a  return  of  capital.  The  question 
then  is  one  of  policy  in  the  company's  finance,  and  in  neither 
case  is  it  a  matter  which  can  be  brought  into  working  costs  and 


180  PRINCIPLES   OF  MINING. 

leave  them  any  value  for  comparative  purposes.  Indeed,  the 
true  cost  of  working  the  ore  from  any  mine  can  only  be  told  when 
the  mine  is  exhausted :  then  the  dividends  can  be  subtracted 
from  the  capital  sunk  and  metal  sold,  and  the  difference  divided 
over  the  total  tonnage  produced. 

The  third  section  of  the  report  affords  wide  scope  for  the 
best  efforts  of  the  administration.  This  portion  of  the  report 
falls  into  three  divisions :  (a)  the  construction  and  equipment 
work  of  the  year,  (6)  the  ore  extraction  and  treatment,  and  (c) 
the  results  of  development  work. 

The  first  requires  a  statement  of  the  plant  constructed,  its 
object  and  accomplishment;  the  second  a  disclosure  of  ton- 
nage produced,  values,  metallurgical  and  mechanical  efficiency. 
The  third  is  of  the  utmost  importance  to  the  stockholder,  and  is 
the  one  most  often  disregarded  and  obscured.  Upon  this  hinges 
the  value  of  the  property.  There  is  no  reason  why,  with  plans 
and  simplicity  of  terms,  such  reports  cannot  be  presented  in  a 
manner  from  which  the  novice  can  judge  of  the  intrinsic  position 
of  the  property.  A  statement  of  the  tonnage  of  ore-reserves 
and  their  value,  or  of  the  number  of  years'  supply  of  the  current 
output,  together  with  details  of  ore  disclosed  in  development 
work,  and  the  working  costs,  give  the  ground  data  upon  which 
any  stockholder  who  takes  interest  in  his  investment  may  judge 
for  himself.  Failure  to  provide  such  data  will  some  day  be  un- 
derstood by  the  investing  public  as  a  prima  fade  index  of  either 
incapacity  or  villainy.  By  the  insistence  of  the  many  engineers 
in  administration  of  mines  upon  the  publication  of  such  data, 
and  by  the  insistence  of  other  engineers  upon  such  data  for 
their  clients  before  investment,  and  by  the  exposure  of  the  delin- 
quents in  the  press,  a  more  practicable  "protection  of  investors " 
can  be  reached  than  by  years  of  academic  discussion. 


CHAPTER  XIX. 

THE  AMOUNT  OF  RISK  IN  MINING  INVESTMENTS. 

RISK  IN  VALUATION  OF  MINES;  IN  MINES  AS  COMPARED  WITH 
OTHER  COMMERCIAL  ENTERPRISES. 

FROM  the  constant  reiteration  of  the  risks  and  difficulties 
involved  in  every  step  of  mining  enterprise  from  the  valuation 
of  the  mine  to  its  administration  as  a  going  concern,  the  im- 
pression may  be  gained  that  the  whole  business  is  one  great 
gamble;  in  other  words,  that  the  point  whereat  certainties 
stop  and  conjecture  steps  in  is  so  vital  as  to  render  the  whole 
highly  speculative. 

Far  from  denying  that  mining  is,  in  comparison  with  better- 
class  government  bonds,  a  speculative  type  of  investment,  it  is 
desirable  to  avow  and  emphasize  the  fact.  But  it  is  none  the 
less  well  to  inquire  what  degree  of  hazard  enters  in  and  how  it 
compares  with  that  in  other  forms  of  industrial  enterprise. 

Mining  business,  from  an  investment  view,  is  of  two  sorts, — 
prospecting  ventures  and  developed  mines;  that  is,  mines 
where  little  or  no  ore  is  exposed,  and  mines  where  a  definite 
quantity  of  ore  is  measurable  or  can  be  reasonably  anticipated. 
The  great  hazards  and  likewise  the  Aladdin  caves  of  mining 
are  mainly  confined  to  the  first  class.  Although  all  mines  must 
pass  through  the  prospecting  stage,  the  great  industry  of  metal 
production  is  based  on  developed  mines,  and  it  is  these  which 
should  come  into  the  purview  of  the  non-professional  investor. 
The  first  class  should  be  reserved  invariably  for  speculators, 
and  a  speculator  may  be  defined  as  one  who  hazards  all  to  gain 
much.  It  is  with  mining  as  an  investment,  however,  that  this 
discussion  is  concerned. 

Risk  in  Valuation  of  Mines.  —  Assuming  a  competent  col- 
lection of  data  and  efficient  management  of  the  property,  the 
risks  in  valuing  are  from  step  to  step :  — 

181 


182  PRINCIPLES   OF  MINING. 

1.  The  risk  of  continuity  in  metal  contents  beyond  sample 

faces. 

2.  The  risk   of  continuity  in  volume  through  the  blocks 

estimated. 

3.  The  risk  of  successful  metallurgical  treatment. 

4.  The  risk  of  metal  prices,  in  all  but  gold. 

5.  The  risk  of  properly  estimating  costs. 

6.  The  risk  of  extension  of  the  ore  beyond  exposures. 

7.  The  risk  of  management. 

As  to  the  continuity  of  values  and  volumes  through  the  esti- 
mated area,  the  experience  of  hundreds  of  engineers  in  hun- 
dreds of  mines  has  shown  that  when  the  estimates  are  based  on 
properly  secured  data  for  "  proved  ore/'  here  at  least  there  is 
absolutely  no  hazard.  Metallurgical  treatment,  if  determined 
by  past  experience  on  the  ore  itself,  carries  no  chance;  and 
where  determined  by  experiment,  the  risk  is  eliminated  if  the 
work  be  sufficiently  exhaustive.  The  risk  of  metal  price  is 
simply  a  question  of  how  conservative  a  figure  is  used  in  estimat- 
ing. It  can  be  eliminated  if  a  price  low  enough  be  taken.  Risk 
of  extension  in  depth  or  beyond  exposures  cannot  be  avoided. 
It  can  be  reduced  in  proportion  to  the  distance  assumed.  Ob- 
viously, if  no  extension  is  counted,  there  is  nothing  chanced. 
The  risk  of  proper  appreciation  of  costs  is  negligible  where  ex- 
perience in  the  district  exists.  Otherwise,  it  can  be  eliminated 
if.  a  sufficiently  large  allowance  is  taken.  The  risk  of  failure 
to  secure  good  management  can  be  eliminated  if  proved  men 
are  chosen. 

There  is,  therefore,  a  basic  value  to  every  mine.  The  "  proved ' ' 
ore  taken  on  known  metallurgical  grounds,  under  known  condi- 
tions of  costs  on  minimum  prices  of  metals,  has  a  value  as  cer- 
tain as  that  of  money  in  one's  own  vault.  This  is  the  value  pre- 
viously referred  to  as  the  "A  "  value.  If  the  price  (and  interest 
on  it  pending  recovery)  falls  within  this  amount,  there  is  no 
question  that  the  mine  is  worth  the  price.  What  the  risk  is  in 
mining  is  simply  what  amount  the  price  of  the  investment  de- 
mands shall  be  won  from  extension  of  the  deposit  beyond  known 


THE  AMOUNT  OF  RISK  IN  MINING  INVESTMENTS.    183 

.exposures,  or  what  higher  price  of  metal  must  be  realized  than 
that  calculated  in  the  "A"  value.  The  demands  on  this  X,  Y 
portion  of  the  mine  can  be  converted  into  tons  of  ore,  life  of  pro- 
duction, or-  higher  prices,  and  these  can  be  weighed  with  the 
geological  weights  and  the  industrial  outlook. 

Mines  compared  to  Other  Commercial  Enterprises.  —  The 
profits  from  a  mining  venture  over  and  above  the  bed-rock  value 
A,  that  is,  the  return  to  be  derived  from  more  extensive  ore- 
recovery  and  a  higher  price  of  metal,  may  be  compared  to  the 
value  included  in  other  forms  of  commercial  enterprise  for  "  good- 
will." Such  forms  of  enterprise  are  valued  on  a  basis  of  the 
amount  which  will  replace  the  net  assets  plus  (or  minus)  an 
amount  for  "good-will/7  that  is,  the  earning  capacity.  This 
good-will  is  a  speculation  of  varying  risk  depending  on  the  char- 
acter of  the  enterprise.  For  natural  monopolies,  like  some  rail- 
ways and  waterworks,  the  risk  is  less  and  for  shoe  factories  more. 
Even  natural  monopolies  are  subject  to  the  risks  of  antagonistic 
legislation  and  industrial  storms.  But,  eliminating  this  class  of 
enterprise,  the  speculative  value  of  a  good-will  involves  a  greater 
risk  than  prospective  value  in  mines,  if  properly  measured ;  be- 
cause the  dangers  of  competition  and  industrial  storms  do  not 
enter  to  such  a  degree,  nor  is  the  future  so  dependent  upon  the 
human  genius  of  the  founder  or  manager.  Mining  has  reached 
such  a  stage  of  development  as  a  science  that  management 
proceeds  upon  comparatively  well-known  lines.  It  is  subject  to 
known  checks  through  the  opportunity  of  comparisons  by  which 
efficiency  can  be  determined  in  a  manner  more  open  for  the  in- 
vestor to  learn  than  in  any  other  form  of  industry.  While  in 
mining  an  estimate  of  a  certain  minimum  of  extension  in  depth, 
as  indicated  by  collateral  factors,  may  occasionally  fall  short,  it 
will,  in  nine  cases  out  of  ten,  be  exceeded.  If  investment  in  mines 
be  spread  over  ten  cases,  similarly  valued  as  to  minimum  of  ex- 
tension, the  risk  has  been  virtually  eliminated.  The  industry, 
if  reduced  to  the  above  basis  for  financial  guidance,  is  a  more 
profitable  business  and  is  one  of  less  hazards  than  competitive 
forms  of  commercial  enterprises. 

In  view  of  what  has  been  said  before,  it  may  be  unnecessary 


184  PRINCIPLES  OF  MINING. 

to  refer  again  to  the  subject,  but  the  constant  reiteration  by 
wiseacres  that  the  weak  point  in  mining  investments  lies  in  their 
short  life  and  possible  loss  of  capital,  warrants  a  repetition  that 
the  A,  B,  C  of  proper  investment  in  mines  is  to  be 'assured,  by 
the  "A"  value,  of  a  return  of  the  whole  or  major  portion  of  the 
capital.  The  risk  of  interest  and  profit  may  be  deferred  to  the 
X,  Y  value,  and  in  such  case  it  is  on  a  plane  with  "good-will." 
It  should  be  said  at  once  to  that  class  who  want  large  returns  on 
investment  without  investigation  as  to  merits,  or  assurance  as  to 
the  management  of  the  business,  that  there  is  no  field  in  this 
world  for  the  employment  of  their  money  at  over  4%. 

Unfortunately  for  the  reputation  of  the  mining  industry, 
and  metal  mines  especially,  the  business  is  often  not  conducted 
or  valued  on  lines  which  have  been  outlined  in  these  chapters. 
There  is  often  the  desire  to  sell  stocks  beyond  their  value.  There 
is  always  the  possibility  that  extension  in  depth  will  reveal  a 
glorious  Eldorado.  It  occasionally  does,  and  the  report  echoes 
round  the  world  for  years,  together  with  tributes  to  the  great 
judgment  of  the  exploiters.  The  volume  of  sound  allures  undue 
numbers  of  the  venturesome,  untrained,  and  ill-advised  public 
to  the  business,  together  with  a  mob  of  camp-followers  whose 
objective  is  to  exploit  the  ignorant  by  preying  on  their  gam- 
bling instincts.  Thus  a  considerable  section  of  metal  mining 
industry  is  in  the  hands  of  these  classes,  and  a  cloud  of  disrepute 
hangs  ever  in  the  horizon. 

There  has  been  a  great  educational  campaign  in  progress 
during  the  past  few  years  through  the  technical  training  of  men 
for  conduct  of  the  industry,  by  the  example  of  reputable  com- 
panies in  regularly  publishing  the  essential  facts  upon  which  the 
value  of  their  mines  is  based,  and  through  understandable  non- 
technical discussion  in  and  by  some  sections  of  the  financial  and 
general  press.  The  real  investor  is  being  educated  to  distin- 
guish between  reputable  concerns  and  the  counters  of  gamesters. 
Moreover,  yearly,  men  of  technical  knowledge  are  taking  a 
stronger  and  more  influential  part  in  mining  finance  and  in  the 
direction  of  mining  and  exploration  companies.  The  net  result 
of  tkese  forces  will  be  to  put  mining  on  a  better  plane. 


CHAPTER  XX. 

THE  CHARACTER,  TRAINING,  AND  OBLIGATIONS  OF  THE  MINING 
ENGINEERING  PROFESSION. 

IN  a  discussion  of  some  problems  of  metal  mining  from  the 
point  of  view  of  the  direction  of  mining  operations  it  may  not 
be  amiss  to  discuss  the  character  of  the  mining  engineering 
]  H'of ession  in  its  bearings  on  training  and  practice,  and  its  rela- 
tions to  the  public. 

The  most  dominant  characteristic  of  the  mining  engineering 
profession  is  the  vast  preponderance  of  the  commercial  over  the 
technical  in  the  daily  work  of  the  engineer.  For  years  a  gradual 
evolution  has  been  in  progress  altering  the  larger  demands  on 
this  branch  of  the  engineering  profession  from  advisory  to 
executive  work.  The  mining  engineer  is  no  longer  the  techni- 
cian who  concocts  reports  and  blue  prints.  It  is  demanded  of 
him  that  he  devise  the  finance,  construct  and  manage  the  works 
which  he  advises.  The  demands  of  such  executive  work  are 
largely  commercial;  although  the  commercial  experience  and 
executive  ability  thus  become  one  pier  in  the  foundation  of 
training,  the  bridge  no  less  requires  two  piers,  and  the  second 
is  based  on  technical  knowledge.  Far  from  being  deprecated, 
these  commercial  phases  cannot  be  too  strongly  emphasized. 
On  the  other  hand,  I  am  far  from  contending  that  our  vocation 
is  a  business  rather  than  a  profession. 

For  many  years  after  the  dawn  of  modern  engineering,  the 
members  of  our  profession  were  men  who  rose  through  the 
ranks  of  workmen,  and  as  a  result,  we  are  to  this  day  in  the 
public  mind  a  sort  of  superior  artisan,  for  to  many  the  engine- 
driver  is  equally  an  engineer  with  the  designer  of  the  engine,  yet 
their  real  relation  is  but  as  the  hand  to  the  brain.  At  a  later 
period  the  recruits  entered  by  apprenticeship  to  those  men  who 
had  established  their  intellectual  superiority  to  their  fellow- 

185 


186  PRINCIPLES  OF  MINING. 

workers.  These  men  were  nearly  always  employed  in  an  advisory 
way  —  subjective  to  the  executive  head. 

During  the  last  few  decades,  the  advance  of  science  and  the 
complication  of  industry  have  demanded  a  wholly  broader  basis 
of  scientific  and  general  training  for  its  leaders.  Executive 
heads  are  demanded  who  have  technical  training.  This  has 
resulted  in  the  establishment  of  special  technical  colleges,  and 
compelled  a  place  for  engineering  in  the  great  universities.  The 
high  intelligence  demanded  by  the  vocation  itself,  and  the  revo- 
lution in  training  caused  by  the  strengthening  of  its  foundations 
in  general  education,  has  finally,  beyond  all  question,  raised  the 
work  of  application  of  science  to  industry  to  the  dignity  of  a  pro- 
fession on  a  par  with  the  law,  medicine,  and  science.  It  demands 
of  its  members  equally  high  mental  attainments,  —  and  a  more 
rigorous  training  and  experience.  Despite  all  this,  industry  is 
conducted  for  commercial  purposes,  and  leaves  no  room  for  the 
haughty  intellectual  superiority  assumed  by  some  professions 
over  business  callings. 

There  is  now  demanded  of  the  mining  specialist  a  wide 
knowledge  of  certain  branches  of  civil,  mechanical,  electrical, 
and  chemical  engineering,  geology,  economics,  the  humanities, 
and  what  not;  and  in  addition  to  all  this,  engineering  sense, 
executive  ability,  business  experience,  and  financial  insight. 
Engineering  sense  is  that  fine  blend  of  honesty,  ingenuity,  and 
intuition  which  is  a  mental  endowment  apart  from  knowledge 
and  experience.  Its  possession  is  the  test  of  the  real  engineer. 
.It  distinguishes  engineering  as  a  profession  from  engineering  as 
a  trade.  It  is  this  sense  that  elevates  the  possessor  to  the  pro- 
fession which  is,  of  all  others,  the  most  difficult  and  the  most 
comprehensive.  Financial  insight  can  only  come  by  experience 
in  the  commercial  world.  Likewise  must  come  the  experience 
in  technical  work  which  gives  balance  to  theoretical  training. 
Executive  ability  is  that  capacity  to  coordinate  and  command 
the  best  results  from  other  men,  —  it  is  a  natural  endowment 
which  can  be  cultivated  only  in  actual  use. 

The  practice  of  mine  engineering  being  so  large  a  mixture  of 
business,  it  follows  that  the  whole  of  the  training  of  this  pro- 


THE  MINING  ENGINEERING  PROFESSION.  187 

fession  cannot  be  had  in  schools  and  universities.  The  commer- 
cial and  executive  side  of  the  work  cannot  be  taught;  it  must  be 
absorbed  by  actual  participation  in  the  industry.  Nor  is  it  im- 
possible to  rise  to  great  eminence  in  the  profession  without 
university  training,  as  witness  some  of  our  greatest  engineers. 
The  university  can  do  much ;  it  can  give  a  broad  basis  of  knowl- 
edge and  mental  training,  and  can  inculcate  moral  feeling, 
which  entitles  men  to  lead  their  fellows.  It  can  teach  the  tech- 
nical fundamentals  of  the  multifold  sciences  which  the  engineer 
should  know  and  must  apply.  But  after  the  university  must 
come  a  schooling  in  men  and  things  equally  thorough  and  more 
arduous. 

In  this  predominating  demand  for  commercial  qualifications 
over  the  technical  ones,  the  mining  profession  has  differentiated 
to  a  great  degree  from  its  brother  engineering  branches.  That 
this  is  true  will  be  most  apparent  if  we  examine  the  course 
through  which  engineering  projects  march,  and  the  demands  of 
each  stage  on  their  road  to  completion. 

The  life  of  all  engineering  projects  in  a  general  way  may  be 
divided  into  five  phases :  *  — 

1.  Determination  of  the  value  of  the  project. 

2.  Determination  of  the  method  of  attack. 

3.  The  detailed  delineation  of  method,  means,  and  tools. 

4.  The  execution  of  the  works. 

5.  The  operation  of  the  completed  works. 

These  various  stages  of  the  resolution  of  an  engineering 
project  require  in  each  more  or  less  of  every  quality  of  intellect, 
training,  and  character.  At  the  different  stages,  certain  of  these 
qualities  are  in  predominant  demand:  in  the  first  stage, 
financial  insight;  in  the  second,  "engineering  sense ";  in  the 
third,  training  and  experience;  in  the  fourth  and  fifth,  executive 
ability. 

A  certain  amount  of  compass  over  the  project  during  the 

*  These  phases  do  not  necessarily  proceed  step  by  step.     For  an  ex- 

Eanding  works  especially,  all  of  them  may  be  in  process  at  the  same  time, 
ut  if  each  item  be  considered  to  itself,  this  is  the  usual  progress,  or  should 
be  when  properly  engineered. 


188  PRINCIPLES   OF  MINING. 

whole  five  stages  is  required  by  all  branches  of  the  engineering 
profession,  —  harbor,  canal,  railway,  waterworks,  bridge,  me- 
chanical, electrical,  etc.;  but  in  none  of  them  so  completely 
and  in  such  constant  combination  is  this  demanded  as  in  mining. 

The  determination  of  the  commercial  value  of  projects  is 
a  greater  section  of  the  mining  engineer's  occupation  than  of 
the  other  engineering  branches.  Mines  are  operated  only  to 
earn  immediate  profits.  No  question  of  public  utility  enters, 
so  that  all  mining  projects  have  by  this  necessity  to  be  from  the 
first  weighed  from  a  profit  point  of  view  alone.  The  determina- 
tion of  this  question  is  one  which  demands  such  an  amount  of 
technical  knowledge  and  experience  that  those  who  are  not 
experts  cannot  enter  the  field,  —  therefore  the  service  of  the 
engineer  is  always  demanded  in  their  satisfactory  solution. 
Moreover,  unlike  most  other  engineering  projects,  mines  have 
a  faculty  of  changing  -owners  several  times  during  their  career, 
so  that  every  one  has  to  survive  a  periodic  revaluation.  From 
the  other  branches  of  engineering,  the  electrical  engineer  is 
the  most  often  called  upon  to  weigh  the  probabilities  of  financial 
success  of  the  enterprise,  but  usually  his  presence  in  this  capacity 
is  called  upon  only  at  the  initial  stage,  for  electrical  enterprises 
seldom  change  hands.  The  mechanical  and  chemical  branches 
are  usually  called  upon  for  purely  technical  service  on  the  demand 
of  the  operator,  who  decides  the  financial  problems  for  himself, 
or  upon  works  forming  but  units  in  undertakings  where  the 
opinion  on  the  financial  advisability  is  compassed  by  some  other 
branch  of  the  engineering  profession.  The  other  engineering 
branches,  even  less  often,  are  called  in  for  financial  advice,  and 
in  those  branches  involving  works  of  public  utility  the  profit- 
and-loss  phase  scarcely  enters  at  all. 

Given  that  the  project  has  been  determined  upon,  and  that 
the  enterprise  has  entered  upon  the  second  stage,  that  of 
determination  of  method  of  attack,  the  immediate  commercial 
result  limits  the  mining  engineer's  every  plan  and  design  to  a 
greater  degree  than  it  does  the  other  engineering  specialists. 
The  question  of  capital  and  profit  dogs  his  every  footstep,  for 
all  mines  are  ephemeral;  the  life  of  any  given  mine  is  short. 


THE  MINING   ENGINEERING  PROFESSION.  189 

Metal  mines  have  indeed  the  shortest  lives  of  any.  While  some 
exceptional  ones  may  produce  through  one  generation,  under 
the  stress  of  modern  methods  a  much  larger  proportion  extend 
only  over  a  decade  or  two.  But  of  more  pertinent  force  is  the 
fact  that  as  the  certain  life  of  a  metal 'mine  can  be  positively 
known  in  most  cases  but  a  short  period  beyond  the  actual  time 
required  to  exhaust  the  ore  in  sight,  not  even  a  decade  of  life 
to  the  enterprise  is  available  for  the  estimates  of  the  mining 
engineer.  Mining  works  are  of  no  value  when  the  mine  is  ex- 
hausted; -the  capital  invested  must  be  recovered  in  very  short 
periods,  and  therefore  all  mining  works  must  be  of  the  most 
temporary  character  that  will  answer.  The  mining  engineer 
cannot  erect  a  works  that  will  last  as  long  as  possible;  it  is  to 
last  as  long  as  the  mine  only,  and,  in  laying  it  out,  forefront  in 
his  mind  must  be  the  question,  Can  its  cost  be  redeemed  in  the 
period  of  use  of  which  I  am  certain  it  will  find  employment? 
If  not,  will  some  cheaper  device,  which  gives  less  efficiency, 
do  ?  The  harbor  engineer,  the  railway  engineer,  the  mechanical 
engineer,  build  as  solidly  as  they  can,  for  the  demand  for  the 
work  will  exist  till  after  their  materials  are  worn  out,  however 
soundly  they  construct. 

Our  engineer  cousins  can,  in  a  greater  degree  by  study  and 
investigation,  marshal  in  advance  the  factors  with  which  they 
have  to  deal.  The  mining  engineer's  works,  on  the  other  hand, 
depend  at  all  times  on  many  elements  which,  from  the  nature 
of  things,  must  remain  unknown.  No  mine  is  laid  bare  to  study 
and  resolve  in  advance.  We  have  to  deal  with  conditions  buried 
in  the  earth.  Especially  in  metal  mines  we  cannot  know,  when 
our  works  are  initiated,  what  the  size,  mineralization,  or  surround- 
ings of  the  ore-bodies  will  be.  We  must  plunge  into  them  and 
learn, — and  repent.  Not  only  is  the  useful  life  of  our  mining 
works  indeterminate,  but  the  very  character  of  them  is  uncertain 
in  advance.  All  our  works  must  be  in  a  way  doubly  tentative, 
for  they  are  subject  to  constant  alterations  as  they  proceed. 

Not  only  does  this  apply  to  our  initial  plans,  but  to  our  daily 
amendment  of  them  as  we  proceed  into  the  unknown.  Mining 
engineering  is,  therefore,  never  ended  with  the  initial  determina- 


190  PRINCIPLES  OF  MINING. 

tion  of  a  method.  It  is  called  upon  daily  to  replan  and  recon- 
ceive,  coincidentally  with  the  daily  progress  of  the  constructions 
and  operation.  Weary  with  disappointment  in  his  wisest  con- 
ception, many  a  mining  engineer  looks  jealously  upon  his  happier 
engineering  cousin,  who/ when  he  designs  a  bridge,  can  know  its 
size,  its  strains,  and  its  cost,  and  can  wash  his  hands  of  it  finally 
when  the  contractor  steps  in  to  its  construction.  And,  above  all, 
it  is  no  concern  of  his  whether  it  will  pay.  Did  he  start  to  build 
a  bridge  over  a  water,  the  width  or  depth  or  bottom  of  which 
he  could  not  know  in  advance,  and  require  to  get  its  cost  back 
in  ten  years,  with  a  profit,  his  would  be  a  task  of  similar  harass- 
ments. 

As  said  before,  it  is  becoming  more  general  every  year  to 
employ  the  mining  engineer  as  the  executive  head  in  the  opera- 
tion of  mining  engineering  projects,  that  is,  in  the  fourth  and 
fifth  stages  of  the  enterprise.  He  is  becoming  the  foreman, 
manager,  and  president  of  the  company,  or  as  it  may  be  contended 
by  some,  the  executive  head  is  coming  to  have  technical  quali- 
fications. Either  way,  in  no  branch  of  enterprise  founded  on 
engineering  is  the  operative  head  of  necessity  so  much  a  technical 
director.  Not  only  is  this  caused  by  the  necessity  of  executive 
knowledge  before  valuations  can  be  properly  done,  but  the  incor- 
poration of  the  executive  work  with  the  technical  has  been 
brought  about  by  several  other  forces.  We  have  a  type  of  works 
which,  by  reason  of  the  new  conditions  and  constant  revisions 
which  arise  from  pushing  into  the  unknown  coincidentally  with 
operating,  demands  an  intimate  continuous  daily  employment 
of  engineering  sense  and  design  through  the  whole  history  of 
the  enterprise.  These  works  are  of  themselves  of  a  character 
which  requires  a  constant  vigilant  eye  on  financial  outcome. 
The  advances  in  metallurgy,  and  the  decreased  cost  of  production 
by  larger  capacities,  require  yearly  larger,  more  complicated, 
and  more  costly  plants.  Thus,  larger  and  larger  capitals  are 
required,  and  enterprise  is  passing  from  the  hands  of  the  individual 
to  the  financially  stronger  corporation.  This  altered  position 
as  to  the  works  and  finance  has  made  keener  demands,  both 
technically  and  in  an  administrative  way,  for  the  highly  trained 


THE  MINING  ENGINEERING  PROFESSION.  191 

man.  In  the  early  stages  of  American  mining,  with  the  moderate 
demand  on  capital  and  the  simpler  forms  of  engineering  involved, 
mining  was  largely  a  matter  of  individual  enterprise  and  owner- 
ship. These  owners  were  men  to  whom  experience  had  brought 
some  of  the  needful  technical  qualifications.  They  usually  held 
the  reins  of  business  management  in  their  own  hands  and  em- 
ployed the  engineer  subjectively,  when  they  employed  him  at 
all.  They  were  also,  as  a  rule,  distinguished  by  their  contempt 
for  university-trained  engineers. 

The  gradually  increasing  employment  of  the  engineer  as 
combined  executive  and  technical  head,  was  largely  of  American 
development.  Many  English  and  European  mines  still  maintain 
the  two  separate  bureaus,  the  technical  and  the  financial.  Such 
organization  is  open  to  much  objection  from  the  point  of  view 
of  the  owner's  interests,  and  still  more  from  that  of  the  engineer. 
In  such  an  organization  the  latter  is  always  subordinate  to  the 
financial  control,  —  hence  the  least  paid  and  least  respected. 
When  two  bureaus  exist,  the  technical  lacks  that  balance  of 
commercial  purpose  which  it  should  have.  The  ambition  of  the 
theoretical  engineer,  divorced  from  commercial  result,  is  com- 
plete technical  nicety  of  works  and  low  production  costs  without 
the  regard  for  capital  outlay  which  the  commercial  experience 
and  temporary  character  of  mining  constructions  demand.  On 
the  other  hand,  the  purely  financial  bureau  usually  begrudges 
the  capital  outlay  which  sound  engineering  may  warrant.  The 
result  is  an  administration  that  is  not  comparable  to  the  single 
head -with  both  qualifications  and  an  even  balance  in  both  spheres. 
In  America,  we  still  have  a  relic  of  this  form  of  administration 
in  the  consulting  mining  engineer,  but  barring  his  functions  as 
a  valuer  of  mines,  he  is  disappearing  in  connection  with  the 
industry,  in  favor  of  the  manager,  or  the  president  of  the  company, 
who  has  administrative  control.  The  mining  engineer's  field 
of  employment  is  therefore  not  only  wider  by  this  general  inclu- 
sion of  administrative  work,  but  one  of  more  responsibility. 
While  he  must  conduct  all  five  phases  of  engineering  projects 
coincidentally,  the  other  branches  of  the  profession  are  more 
or  less  confined  to  one  phase  or  another.  They  can  draw  sharper 


192  PRINCIPLES   OF  MINING. 

limitations  of  their  engagements  or  specialization  and  confine 
themselves  to  more  purely  technical  work.  The  civil  engineer 
may  construct  railway  or  harbor  works;  the  mechanical  engineer 
may  design  and  build  engines;  the  naval  architect  may  build 
ships;  but  given  that  he  designed  to  do  the  work  in  the  most 
effectual  manner,  it  is  no  concern  of  his  whether  they  subsequently 
earn  dividends.  He  does  not  have  to  operate  them,  to  find  the 
income,  to  feed  the  mill,  or  sell  the  product.  The  profit  and  loss 
does  not  hound  his  footsteps  after  his  construction  is  complete. 

Although  it  is  desirable  to  emphasize  the  commercial  side  of 
the  practice  of  the  mining  engineer's  profession,  there  are  other 
sides  of  no  less  moment.  There  is  the  right  of  every  red-blooded 
man  to  be  assured  that  his  work  will  be  a  daily  satisfaction  to 
himself;  that  it  is  a  work  which  is  contributing  to  the  welfare 
and  advance  of  his  country ;  and  that  it  will  build  for  him  a  posi- 
tion of  dignity  and  consequence  among  his  fellows. 

There  are  the  moral  and  public  obligations  upon  the  pro- 
fession. There  are  to-day  the  demands  upon  the  engineers  which 
are  the  demands  upon  their  positions  as  leaders  of  a  great  industiy . 
In  an  industry  that  lends  itself  so  much  to  speculation  and 
chicanery,  there  is  the  duty  of  every  engineer  to  diminish  the 
opportunity  of  the  vulture  so  far  as  is  possible.  Where  he  can 
enter  these  lists  has  been  suggested  in  the  previous  pages.  Fur- 
ther than  to  the  "investor"  in  mines,  he  has  a  duty  to  his  broth- 
ers in  the  profession.  In  no  profession  does  competition  enter 
so  obscurely,  nor  in  no  other  are  men  of  a  profession  thrown  into 
such  terms  of  intimacy  in  professional  work.  From  these  causes 
there  has  arisen  a  freedom  of  disclosure  of  technical  results  and 
a  comradery  of  members  greater  than  that  in  any  other  pro- 
fession. No  profession  is  so  subject  to  the  capriciousness  of 
fortune,  and  he  whose  position  is  assured  to-day  is  not  assured 
to-morrow  unless  it  be  coupled  with  a  consideration  of  those 
members  not  so  fortunate.  Especially  is  there  an  obligation  to 
the  younger  members  that  they  may  have  opportunity  of  training 
and  a  right  start  in  the  work. 

The  very  essence  of  the  profession  is  that  it  calls  upon  its 
members  to  direct  men.  They  are  the  officers  in  the  great  in- 


THE  MINING   ENGINEERING  PROFESSION.  193 

dustrial  army.  From  the  nature  of  things,  metal  mines  do  not, 
like  our  cities  and  settlements,  lie  in  those  regions  covered  deep 
in  rich  soils.  Our  mines  must  be  found  in  the  mountains  and 
deserts  where  rocks  are  exposed  to  search.  Thus  they  lie  away 
from  the  centers  of  comfort  and  culture,  —  they  are  the  outposts 
of  civilization.  The  engineer  is  an  officer  on  outpost  duty,  and 
in  these  places  he  is  the  camp  leader.  By  his  position  as  a  leader 
in  the  community  he  has  a  chieftainship  that  carries  a  responsi- 
bility besides  mere  mine  management.  His  is  the  responsibility 
of  example  in  fair  dealing  and  good  government  in  the  community. 

In  but  few  of  its  greatest  works  does  the  personality  of  its 
real  creator  reach  the  ears  of  the  world;  the  real  engineer  does 
not  advertise  himself.  But  the  engineering  profession  generally 
rises  yearly  in  dignity  and  importance  as  the  rest  of  the  world 
learns  more  of  where  the  real  brains  of  industrial  progress  are. 
The  time  will  come  when  people  will  ask,  not  who  paid  for  a 
thing,  but  who  built  it. 

To  the  engineer  falls  the  work  of  creating  from  the  dry  bones 
of  scientific  fact  the  living  body  of  industry.  It  is  he  whose 
intellect  and  direction  bring  to  the  world  the  comforts  and  neces- 
sities of  daily  need.  Unlike  the  doctor,  his  is  not  the  constant 
struggle  to  save  the  weak.  Unlike  the  soldier,  destruction  is  not 
his  prime  function.  Unlike  the  lawyer,  quarrels  are  not  his 
daily  bread.  Engineering  is  the  profession  of  creation  and  of 
construction,  of  stimulation  of  human  effort  an'd  accomplish- 
ment. 


INDEX. 


Accounts,  169. 

Administration,  161,  169,  178. 
Administrative  reports,  178. 
Air-compression,  146. 

-drills,  147. 

Alteration,  secondary,  24,  25,  26,  30. 
Alternative  shafts  to  inclined  deposit, 

63. 
Amortization  of  capital  and  interest, 

42. 
Animals  for  underground  transport, 

134. 
Annual  demand  for  base  metals,  38. 

report,  179. 
Artificial  pillars,  121. 
Assay  foot,  10. 

inch,  10. 

of  samples,  7. 

plans,  1,  7. 
Assaying,  177. 
A  value  of  mine,  56. 
Averages,  calculation,  1,  8. 

Bailing,  143. 
Balance  sheet,  179. 
Basic  price,  36,  37. 

value  of  mine,  182. 
Benches,  95. 

Bend  in  combined  shafts,  59. 
Bins,  84. 

Blocked-out  ore,  18. 
Blocks,  13. 
Bonanzas,  origin,  28. 
Bonus  systems  of  work,  167. 
Breaking  ore,  115. 
Broken  Hill,  levels,  119. 

ore-pillars,  120. 
Bumping-trough,  89,  136. 

Cable-ways,  135. 

Cages,  132. 

Calculation  of  averages,  1,  8. 

of  quantities  of  ore,  13. 
Capital  expenditure,  170. 


Caving  systems,  122. 
Churn-drills,  92. 

Chutes,  loading,  in  vertical  shaft,  86. 
Classification  of  ore  in  sight,  13,  16. 
Combined  shaft,  58,  67,  68,  69,  70,  72. 

stopes,  96,  101. 

Commercial  value  of  projects,  deter- 
mination, 188. 
Compartments  for  shaft,  76. 
Compressed-air  locomotives,  135. 
-air  pumps,  141. 

vs.  electricity  for  drills,  145. 
Content,    average   metal,    determin- 
ing, 1. 

metal,  differences,  6. 
Contract  work,  165. 
Copper,  annual  demand,  38. 
deposits,  1. 
ores,  enrichment,  30. 
Cost  of  entry  into  mine,  65. 
of  equipment,  156. 

production,  38,  39. 
per  foot  of  sinking,  64. 
working,  40,  170. 
Cribs,  103,  107. 
Crosscuts,  86. 

Cross-section  of  inclined  deposit  which 
must  be  attacked  in  depth,  68. 
showing  auxiliary  vertical  out- 
let, 66. 

Crouch,  J.  J.,  145. 
Cubic  feet  per  ton  of  ore,  14,  15. 
foot  contents  of  block,  13. 

Deep-level  mines,  60. 
Demand  for  metals,  35. 
Departmental  dissection  of  expendi- 
tures, 171. 
Deposits,  in  situ,  1. 

ore,  classes,  24. 

regularity,  88. 

size,  30. 

structure,  24.. 
Depth  of  exhaustion,  21,  32. 


195 


196 


INDEX. 


Determination  of  average  metal  con- 
tents of  ore,  3. 

Development    in    early    prospecting 

stage,  92. 

in  neighboring  mines,  21,  31. 
of  mines,  58,  74,  84. 

Diamond-drilling,  93. 

Diluting  narrow  samples  to  a  stop- 
ing  width,  11. 

Dip,  89. 

Direct-acting  steam-pumps,  140. 

Distribution  of  values,  30. 

Dividend,  annual,  present  value,  46. 

Dommeiler,  145. 

Down  holes,  100. 

Drainage  138. 

comparison   of  different  systems, 

143. 
systems,  140. 

Drifts,  87. 

Drill,  requirements,  145. 

Drilling,  92,  145. 

Drives,  87. 

Dry  walling  with  timber  caps,  91. 

Efficiency,  factors  of,  162. 

of  mass,  162. 
Electrical  haulage,  135. 

pumps,  141. 

Electricity  for  drills,  145. 
Engine,  size  for  winding  appliances, 

131. 

Engineer,  mining,  as  executive,  190. 
Engineering  projects,  phases  of,  187. 
Enrichment,  27,  28,  29. 

at  cross-veins,  24. 
Entry,  to  mine,  58. 

to  vertical  or  horizontal  deposits, 

62,  63. 
Equipment,  cost,  156. 

improvements,  152. 

mechanical,  138,  145. 
Erosion,  26,  29. 
Error,  percentage  in  estimates  from 

sampling,  1,  11. 
Escape,  73. 

Examination  of  mining  property,  54. 
Excavation,  supporting,  103. 
Exhaustion,  depth,  32. 
Expenditures,      departmental      dis- 
section, 171. 

mine,  170. 
Extension  in  .depth,  21,  22,  28. 


Factor  of  safety  in  calculating  aver- 
ages of  samples,  12. 
Filling,  112. 

system    combined    with    square- 
setting,  111. 
with     broken     ore     subsequently 

withdrawn,  112. 
waste,  107. 
Fissure  veins,  24. 
Fissuring,  23. 

depth,  30. 

Fixed  charges,  154,  170. 
Flat-back  stope,  98,   100,   110. 
Flexibility  in  drainage  system,  138. 
Floors,  31. 
Folding,  23. 
Foot-drilled  system  of  contract  work, 

166. 
-hole    system    of    contract    work, 

166. 
of    advance    system    of    contract 

work,  166. 
value,  10. 

Fraud,  precautions  against  in  sam- 
pling, 7. 

General  expenses,  173. 
Gold  deposits,  1. 

deposits,  alteration,  29,  30. 

enrichment,  28. 

Hammer  type  of  drill,  147,  148,  149. 
Hand-drilling,  149. 

-trucking,  133. 
Haulage,  electrical,  135. 

equipment  in  shaft,  132. 

mechanical,  134. 

Hole  system  of  contract  work,  165. 
Horizons  of  ore-deposits,  26. 
Horizontal  deposits,  entry,  62. 

stope,  98. 

filled  with  waste,  108. 
Hydraulic  pumps,  142. 

Impregnation  deposits,  24. 

Inch,  assay,  10. 

Inclined  deposits  to  be  worked  from 

outcrop  or  near  it,  62. 
deposits  which  must  be  attacked  in 

depth,  67. 
shaft,  64. 

Inclines,  65,  66,  67,  68. 
capacity,  78. 


INDEX. 


197 


Infiltration  type  of  deposits,  24. 
Intelligence  as  factor  of  skill,    163, 

164. 

Interest  calculations  in  mine  valua- 
tion, 43. 

Intervals,  level,  88,  89. 
Inwood's  tables,  46,  47. 
Iron  hat,  27. 

leaching,  27. 
Ivanhoe  mine,  West  Australia,  112. 

Kibble,  132. 

Labor,  general  technical  data,  1-76. 

handling,  161. 

unions,  167. 

Lateral  underground  transport,  133. 
Le  Roi  mine,  112. 
Lead,  annual  demand,  38. 

deposits,  1. 

enriching,  27. 

prices,  1884-1908,  36. 

-zinc  ores,  enrichment,  30. 
Lenses,  24. 
Levels,  87. 

intervals,  88,  89. 

of  Broken  Hill,  119. 

protection,  90. 
Life,  in  sight,  44. 

of  mine,  157. 

Locomotives,  compressed-air,  135. 
Lode  mines,  valuation,  1. 
Lodes,  24. 
Long- wall  stope,  98. 

Machine-drill,  performance,  149. 

drilling,  145. 

vs.  hand-drilling,  149. 
Management,  mine,  161. 
Matte,  123. 

Mechanical    efficiency    of    drainage 
machinery,  139. 

equipment,  124,  134,  138,  145. 
Men  for  underground  transport,  133. 
Metal   content,   determining,    1,    3. 

contents,  differences,  6. 

demand  for,  35. 

mine,  value,  1. 

price,  35,  37. 

Mines  compared  to  other  commer- 
cial enterprises,  183. 

equipment,  124. 

expenditures,  170. 


Mines  —  continued. 

life  of,  157. 

metal,  value  of,  1. 

of  moderate  depths,  62. 

to  be  worked  to  great  depths,  62, 
69. 

valuation,  1,  13,  21,  34,  42,  51. 
Mining  engineering  profession,  185. 
Mt.  Cenis  tunnel,  145. 

Morgan  gold  mine,  26. 

Normal  price,  36,  37. 

Obligations    of    engineering    profes- 
sion, 192. 
Openings,    position    in    relation    to 

secondary  alteration,  23,  25. 
Ore,  average  width  in  block,  13. 

blocked-out,  17. 

-bodies,  23. 
shapes,  8,. 

-breaking,  methods,  94,  95-. 

calculation  of  quantities  of,  13. 

-chutes  in  shrinkage-stoping,  115. 

-deposits,  classes,  24. 

determination    of    average    metal 
contents,  3. 

developed,  17. 

developing,  17. 

expectant,  17. 

in  sight,  16,  17,  20. 

sight,  classification,  13,  16. 

-pillars,  118,  119. 

support  in  narrow  stopes,  118. 

-shoots,  23. 

weight  of  a  cubic  foot,  14. 

width  for  one  sample,  5. 
Origin  of  deposit,  23. 
Outcrop  mines,  60. 
Output,  factors  limiting,  155. 

giving  least  production  cost,  154. 

maximum,  determination,  153. 
Overhand  stopes,  96,  98,  99. 
Overproduction  of  base  metal,  158. 
Oxidation,  30. 

Patchwork  plant,  mechanical  ineffi- 
ciency of,  158. 
Pay  areas,  formation,  23. 
Pillars,  artificial,  121. 
Positive  ore,  17,  20. 

value  of  metal  mine,  1. 
Possible  ore,  17. 


198 


INDEX. 


Power  conditions,  139. 

general  technical  data,  176. 

sources,  126. 

transmission,  125,  126,  127,  145. 
Preliminary  inspection,  55. 
Previous  yield,  3. 
Price  of  metals,  35. 
Probable  ore,  17,  19,  20,  21. 
Producing  stage  of  mine,  58. 
Production,  cost,  38,  39. 
Profit  and  loss  account,  179. 

factors  determining,  2. 

in  sight,  16. 

Proportional  charges,  170. 
Prospecting  stage  of  mine,  58. 
Prospective  ore,  19. 

value,  21. 

Protection  of  levels,  90. 
Proved  ore,  19,  21. 
Pumping  systems,  140. 
Pumps,  compressed-air,  141. 

electrical,  141. 

hydraulic,  142. 

rod-driven,  142. 

Ratio  of  output  to  mine,  153. 
Recoverable  percentage  of  gross  as- 
say value,  34. 
Recovery  of  ore,  107. 
Rectangular  shaft,  74. 
Redemption  of  capital  and  interest, 

42. 

Reduction  of  output,  158. 
Regularity  of  deposit,  88. 
Reliability  of  drainage  system,  139. 
Replacement,  24. 
Reports,  56. 

administrative,  178. 
Resuing,  101. 
Revenue  account,  179. 
Rill-cut  overhand  stope,  99. 

method  of  incline  cuts,  100. 

-stopes,  98,  110. 

filled  with  waste,  108. 

-stoping,  96,  98,  99,  100,  137. 
Rises,  89,  91. 
Risk  in  mining  investments,  181. 

in  valuation  of  mines,  181. 
Roadways,  protecting  in  shrinkage- 

stoping,  114. 
Rod-driven  pumps,  142. 
Rotary  steam-pumps,  140. 
Round  vertical  shafts,  74. 


Runs  of  value,  8. 
test-treatment,  3. 

Safety,     factor     of,     in     calculating 

averages  of  samples,  12. 
Sample,  assay  of,  7. 

average  value.,  9. 

narrow,  diluting  to  a  stoping  width, 
11. 

sections,  5,  6. 

taking,  physical  details,  6. 

manner  of  taking,  4. 
Sampling,  1,  3,  4,  5,  56,  177. 

accuracy,  5. 

percentage   of  error  in   estimates 
from,  11. 

precautions  against  fraud,  7. 
Saving  of  fixed  charges,  155. 
Secondary  alteration,  24,  25,  26,  30. 

enrichment,  21. 
Security  of  investment,  158. 
Self-dumping  skip,  77. 
Sets,  91. 
Shafts,  62,  64-70. 

arrangement    for    very    deep    in- 
»  clined  shafts,  71. 

compartments,  59,  78 

different  depths,  60. 

haulage,  129. 

location,  70. 

number,  72. 

output  capacity,  77. 

shape,  74. 

size,  76,  79. 
Shrinkage-stope,  114,  115. 

-stoping,  112. 
advantages,  117. 
disadvantages,  116. 
when  applicable,  116. 
Silver  deposits,  1. 

deposits,  enrichment,  28,  30. 

prices,  38. 
Sinking,  speed,  80. 
Size  of  deposit,  30. 
Skill,  effect  on  production  cost,  163. 
Skips,  77,  84,  132. 

balanced,  129. 

haulage  in  vertical  shaft,  85. 
Sollars,  109. 

Solubility  of  minerals,  27. 
Specific  volume  of  ores,  14. 
Speculative  values  of  metal  mine,  1. 

value  of  mine,  57. 


INDEX. 


199 


Spelter,  annual  demand,  38. 
Square-set,  103,  104. 

-set  timbering,  104. 
Stations,  84. 

arrangement  for  skip  haulage  in 

vertical  shaft,  85,  87. 
Steam-pumps,  direct,  140. 
Steepening   winzes   and   ore   passes, 

111. 
Stope  filled  with  broken  ore,  113. 

minimum  width,  101. 
Stoping,  89,  94. 

contract  systems,  166. 
Storing  metal,  158. 
Structural  character  of  deposit,  23. 
Structure  of  deposit,  24. 
Stull  and  waste  pillars,  121. 

support     with     waste     reenforce- 
ment,  120. 

-supported  stope,  104. 
Stulls,  103. 

wood,  91. 
Subheading,  90. 
Sublevel  caving  system,  122. 
Subsidiary  development,  84. 
Superficial  enrichment,  29. 
Supplies,  general  technical  data,  176. 
Support  by  pillars  of  ore,  118. 
Supporting  excavation,  103. 
Surveys,  176. 
Suspense  charges,  170. 

Test  parcels,  4. 

sections,  6. 

-treatment  runs,  3. 
Timber,  cost,  77. 
Timbered  shaft  design,  75. 
Timbering,  103,  112. 
Tin,  annual  demand,  38. 

deposits,  1. 

ore,  migration  and  enrichment,  29. 
Tools,  128. 
Top  slicing,  123. 
Tracks,  135. 

Transport  in  stopes,  136. 
Tunnel  entry,  81. 

feet  paid  for  in  10  years,  82. 

size,  82. 

Underhand  stopes,  96,  98. 
Uppers,  100. 


Valuation,  mine,   2,   13,  21,  34,  42, 

51. 

of  lode  mines,  1. 
mines,  risk  in,  181. 
mines  with  little  or  no   ore   in 

sight,  51. 

on  second-hand  data,  52. 
Value,  average,  of  samples,  9. 

discrepancy     between     estimated 

and  actual,  12. 
distribution,  31. 
of  extension  in  depth,  estimating, 

22. 

positive,  of  metal  mine,  1. 
present,  of  an  annual  dividend,  46. 
of  $1  or  £1,  payable  in  —  years, 

47. 

runs  of,  8. 

speculative,  of  metal  mine,  1. 
Valuing  ore  in  course  of  breaking, 

102. 

Ventilation,  72,  73. 
Vertical  deposits,  entry,  62. 
interval  between  levels,  88. 
shafts,  62-70,  72,  85,  86. 

capacity,  78. 
Volume,  specific,  of  ores,  14. 

Waste-filled  stope,  109. 

Water-power,  126. 

Weight  per  cubic  foot    of   ore,   14, 

15. 

Weindel,  Caspar,  145. 
Whiting  hoist,  131. 
Width  of  ore  for  one  sample,  5. 
Winding  appliances,  129. 
Winzes,  89,  91. 

in  shrinkage-stoping,  113. 

to  be  used  for  filling,  107. 
Working  cost,  40,  170. 

inherent   limitations   in   accuracy 
of,  174. 

sheets,  176. 
Workshops,  151. 

Yield,  previous,  3. 

Years  of  life  required  to  yield  —  % 
interest,  48. 

Zinc  deposits,  1. 
leaching,  27. 


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LIBRARY,  UNIVERSITY  OF  CALIFORNIA,  DAVIS 

Book  Slip-50m-12,'64  (F772s4 )  458 


361879 

Hoover,  H.C. 

Principles  of 
mining . 

PHYSICAL 

SCIENCES 

LIBRARY 


H7 


117500665  1387 


LIBRARY 

UNIVERSITY  OF  CALIFORNIA 
DAVIS 


361879 


Hoover,  H.C. 

Principles  of  mining 


Call  Number: 

TN1U5 
H? 


